Infrared And Ultraviolet Spectra Of Diborane(6): B H
Articlepubs.acs.org/JPCAInfrared and Ultraviolet Spectra of Diborane(6): B2H6 and B2D6Yu-Chain Peng,† Sheng-Lung Chou,† Jen-Iu Lo,† Meng-Yeh Lin,† Hsiao-Chi Lu,† Bing-Ming Cheng,*,†and J. F. Ogilvie*,‡†National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, TaiwanEscuela de Quimica, Universidad de Costa Rica, Ciudad Universitaria Rodrigo Facio, San Pedro de Montes de Oca, San Jose11501-2060, Costa Rica‡S Supporting Information*ABSTRACT: We recorded absorption spectra of diborane(6), B2H6 and B2D6,dispersed in solid neon near 4 K in both mid-infrared and ultraviolet regions. Forgaseous B2H6 from 105 to 300 nm, we report quantitative absolute cross sections;for solid B2H6 and for B2H6 dispersed in solid neon, we measured ultravioletabsorbance with relative intensities over a wide range. To assign the mid-infraredspectra to specific isotopic variants, we applied the abundance of 11B and 10B innatural proportions; we undertook quantum-chemical calculations of wavenumbersassociated with anharmonic vibrational modes and the intensities of the harmonicvibrational modes. To aid an interpretation of the ultraviolet spectra, we calculatedthe energies of electronically excited singlet and triplet states and oscillator strengthsfor electronic transitions from the electronic ground state. INTRODUCTIONHere we report our analysis of the infrared and ultravioletabsorption spectra of diborane(6) dispersed in solid neon at 4K and the quantitative ultraviolet spectrum of gaseous diborane,complemented with the aid of quantum-chemical calculations.In a probe of the nature of the primary and secondary productsof a photochemical reaction, an analysis of their infrared spectrarequires a knowledge of the infrared spectra of the precursor orreactant; effective photolytic operations require a knowledge ofthe ultraviolet spectra of that precursor. For the purpose of ourexperiments on diborane(6) dispersed in solid neon thatyielded our discovery and identification of diborane(4),1 wehence investigated the infrared and ultraviolet spectra of thatparent compound under the most appropriate conditions. Theinfrared spectra of gaseous and crystalline diborane have beenreported in detail,2 which led to an empirically derivedharmonic or quadratic force field,3 but the published ultravioletspectra of diborane have poor quality resulting from theprimitive conditions of their measurements before year 1950.4,5For a sample of diborane that contains boron in naturalabundance with two stable isotopic variants, 0.801 11B and0.199 10B, the effective ratio of relative abundance of species11B2H6/10B11BH6/10B2H6 is hence about 16:8:1. For diboranedispersed in solid neon at 4 K, the infrared spectral lines arenarrow and well resolved, allowing accurate measures of theisotopic shifts from the dominant species, 11B2H6, to theisotopic variants 10B2H6 and 11B10BH6. In the infrared spectra,the properties of diborane-d6 are equally important in theanalysis of the spectra of its photochemical products withisotopic boron atomic centers in the same proportions. Incontrast, the absorption in the ultraviolet region is practicallycontinuous from an apparent onset about 35 000 cm 1 to ourlimit of observations about 95 000 cm 1; under theseconditions quantum-chemical calculations might aid theinterpretation of these spectra. 2016 American Chemical Society EXPERIMENTSFor the measurements of infrared absorption spectra, a gaseoussample that was mixed well, containing diborane(6) and neonin great excess, was deposited on a KBr window cooled to 4 Kin a closed-cycle cryostat (Janis RDK-415), which wasevacuated to less than 1.3 10 6 Pa with a turbomolecularpump backed with a scroll pump.6 This cryostat was situated onthe plate of a differential rotary-seal stage with rotatable angle360 ; the KBr window can thus be rotated freely to facedeposition or photolysis or detection ports. The rate ofdeposition was regulated between 70 and 130 μL s 1 andmonitored with a flow transducer. The duration of depositionwas generally 60 180 min. Infrared absorption spectra wererecorded with an interferometric infrared spectrometer(Bomem DA8, KBr beamsplitter, HgCdTe detector cooled to77 K, mid-infrared spectral range 500 5000 cm 1) involving1000 scans at resolution 0.04 cm 1.We measured the ultraviolet absorption spectra of gaseousand condensed samples with light from a synchrotron source;the apparatus for this work is described elsewhere.7 Theultraviolet light was dispersed with a monochromator (focallength 6 m) on the high-flux cylindrical-grating monochromator(CGM) at beamline BL03 of a storage ring (electron energy 1.5Received: May 21, 2016Revised: June 27, 2016Published: June 28, 20165562DOI: 10.1021/acs.jpca.6b05150J. Phys. Chem. A 2016, 120, 5562 5572
ArticleThe Journal of Physical Chemistry AFigure 1. Infrared absorption spectra of diborane(6) dispersed in neon (1:1000) in range 700 3700 cm 1 at 4 K for (a) B2H6 and (b) B2D6.Figure 2. Infrared absorption spectra of B2H6 dispersed in neon (1:1000) at 4 K in range/cm 1 (a) 965 985, (b) 1168 1188, (c) 1590 1610, (d)1830 1900, (e) 2340 2360, and (f) 2510 2650 cm 1.For the measurements of ultraviolet absorption spectra in acondensed phase, a cryostat was used instead of a gas cell. Agaseous sample was deposited onto a rotatable LiF windowmaintained about 4 K with another refrigerator system (JanisRDK-415). The transmitted light was incident on a glasswindow coated with sodium salicylate; the converted visiblelight was measured with a photomultiplier tube. The gasmixtures were prepared according to standard manometricprocedures in a UHV gas-handling system.Ne (99.999%, Scott Specialty Gases) was used withoutfurther purification. B2H6 or B2D6 (Voltaix, chemical puritiesB2H6 99.99% and B2D6 99.8%) was received as 10% in He,which was pumped away at 77 K before use.GeV) named Taiwan Light Source, at National SynchrotronRadiation Research Center (NSRRC). For the gaseous sample,the light passed through an absorption gas cell equipped withtwo LiF end-windows and was incident on a glass windowcoated with sodium salicylate; in this work, two gas cells withpath lengths of 75.0 and 20.0 mm were used. The convertedvisible light was measured (photomultiplier tube, HamamatsuR943-02) in a photon-counting mode. The density of the gaswas determined from the pressure recorded with a capacitancemanometer (MKS, Baratron) and the temperature monitoredwith a thermocouple.The absorption was measured at spectralresolution 0.1 nm; the accuracy of the reported spectralpositions is 0.04 nm.5563DOI: 10.1021/acs.jpca.6b05150J. Phys. Chem. A 2016, 120, 5562 5572
ArticleThe Journal of Physical Chemistry AFigure 3. Infrared absorption spectra of B2D6 dispersed in neon (1:1000) at 4 K in range/cm 1 (a) 715 735, (b) 872 880, (c) 1193 1206, (d)1765 1800, (e) 1840 1865, and (f) 1960 2015 cm 1. centrosymmetric conformations of 10B2H6 and 11B2H6 atequilibrium according to point group D2h Vh dictate thatnine modes are active in Raman scattering and eight modes ininfrared absorption; mode ν5, symmetry class Au, is inactive ineither effect. The appearance of many lines interpreted ascombinations of modes active in absorption and scattering,however, enables estimates of the participating Raman modes.Although the nuclear arrangement of 10B11BH6 according topoint group C2v is not centrosymmetric, such that of 18 modesall but 2 of symmetry class A2, ν8 and ν9, are formally active ininfrared spectra, the dissimilarity with 11B2H6 is weak; few ofthe additional modes might have intensity comparable with the8 modes of the latter, consistent with our calculations. Ouranalysis of our newly recorded spectra is assisted by thereported spectra of diborane in both gaseous and crystallinephases for both B2H6 and B2D6 in natural abundance and 10Benriched to 96%;2 these conditions were favorable for theobservation of most bands or lines in the active infrared modesin the three species for B with either H or D. As many lines inabsorption by B2H6 or B2D6 dispersed in solid neon havewidths comparable with the maximum spectral resolutionpracticable for our recording of these spectra, a saturation ofabsorption causes distortion of lines and inaccurate ratios oftheir statures (net maximum absorbance relative to a baseline);for this reason the apparent ratios of those intensities differfrom the formal ratio of relative abundances, but the trends areclear.Our spectrum of B2H6 in natural abundance in solid neon at4 K displays many absorption features, listed in Table 1, inabout 13 distinct sets, classified according to the vibrationalmodes in the appropriate order according to symmetry species.In many cases, the proximity and ratios of stature enable a clearCALCULATIONSThe wavenumbers of the harmonic and anharmonic vibrationalmodes of diborane(6) were calculated with program Gaussian09,8 the B3LYP method, and basis set 6-311 G** (B3LYP/6311 G**). The vertical singlet and triplet excitation energiesof diborane were predicted with two methods, the TDDFTB3LYP method with aug-cc-pVTZ basis set (TDDFT-B3LYP/aug-cc-pVTZ) and the EOM-CCSD method with 6-311G**basisset (EOM-CCSD/6-311 G**). The singlet and tripletexcitation energies were calculated also with program Dalton2014 with basis aug-cc-pVTZ with a geometry optimized atMC-SCF level.9 RESULTSAnalysis of Infrared Spectra of Diborane. Figure 1shows spectra of B2H6 and B2D6 over the recorded range, 700 3700 cm 1, in which significant measurable absorption featuresappear; Figure 2 for B2H6 and Figure 3 for B2D6 showexpanded regions containing notable features. Table 1 presentsa list of wavenumbers of absorption lines in infrared spectra ofB2H6 in its isotopic variants dispersed in Ne at 4 K with acomparison of published data for gaseous and crystallinediborane;2 Table 2 presents a similar list for B2D6. Someassignments of combination modes in Table 1 and Table 2 aretentative because the wavenumbers of the modes inactive ininfrared absorption are unknowable directly. In specifying thesevibrational modes, we apply a systematic sequence according tosymmetry classes in order Ag, Au, B1g, B1u, B2g, B2u, B3g, and B3u,different from an erratic order used in preceding work.2,3 Of 18fundamental modes of internal vibration expected for anonlinear molecule comprising eight atomic centers, the5564DOI: 10.1021/acs.jpca.6b05150J. Phys. Chem. A 2016, 120, 5562 5572
ArticleThe Journal of Physical Chemistry ATable 1. Wavenumbers/cm 1 of Lines in Infrared Absorption Spectra of B2H6 1:1000 in Ne at 4 K for Indicated IsotopicVariants of B, as 10B or 11B, Compared with Assigned Modes in Gaseous and Crystalline Phasesa,b,cB2H6 gaseousbB2H6 in 0ν1816031607158515861589ν17185418451852ν5 ν1518841880.41886.7ν8185410,11B2H6 crystallineb185418791883.9modeν13 ν151996.16?2356.172357.322343ν3 ν182355ν4 .6ν16260926232597.12607.82611.4ν12A question mark (?) indicates a line or attribution uncertain because of small intensity. bFrom ref 2. cThe number of the mode as νn pertains to11B2H6 unless wavenumbers for only 10B11B2H6 appear in that particular row of the table. dRelative statures to the line at 1597.73 cm 1 are listed inTable S7 in Supporting Information.aassignment to triplets of isotopic boron species containing 11B2,11 10B B, and 10B2, generally in order of increasing wavenumber,although in some cases the small relative abundance of the twocarriers 10B2H6 and 10B2D6 precludes the detection of theirweakest lines. Apart from the fact that our calculations in Table3 apply to free molecules whereas our samples for which thesespectra are recorded contain diborane molecules constrainedwithin a lattice of neon atoms, the calculated isotopic shiftsinvolving boron nuclei are much better reproduced than thecalculated absolute wavenumbers of the lines. A prominentfeature in many parts of the spectra of both B2H6 and B2D6 isthe appearance of doublets or triplets of the isotopic triplets.For instance, Figure 2a,b shows two sets of such triplets ofB2H6 near 975 and 1172 cm 1, assigned to fundamental modesν9 and ν18, respectively. The intense features between 1170 and1180 cm 1, shown in Figure 2b, exhibit an exemplary patternthat is directly assignable as three prominent doublets withrelative statures decreasing with increasing wavenumber; twolines of large stature at 1172.1 and 1173.1 cm 1 are attributedappropriately to 11B2H6, two lines of moderate stature at 1174.7and 1175.6 cm 1 are attributed to 10B11BH6, and two weak linesat 1178.6 and 1179.5 cm 1 are attributed to 10B2H6. Theintervals within the three doublets have mean 0.95 0.04 cm 1.Of the two components of each such doublet, the stature of theline at smaller wavenumber is about 1.1 times that of the line atlarger wavenumber. The wavenumber differences of the othertwo more intense lines from that at 1172.1 cm 1 are 2.6 and 6.4cm 1; according to Table S3 (Supporting Information), thoseshifts are calculated to be 2.4 and 6.5 cm 1, respectively, insatisfactory agreement. Lines at 1172.7, 1175.6, and 1179.1cm 1 might be additional members that would imply a triplet,rather than a doublet, in each case; these weak lines have acommon separation, 0.6 cm 1, from the major lines andconsistent ratios of stature. Other weak lines between 1168.27and 1177.80 cm 1 invoke no obvious assignment; anotherdoublet, barely resolved at 1187.2 and 1187.4 cm 1, is alsounassigned, but all these lines might be associated withvibrational mode ν18 or combinations of other modes inFermi resonance thereof.The region of most intense absorption at about 1600 cm 1,shown in Figure 2c, comprises 34 identified and measuredcomponents. Unlike the region near 1175 cm 1, in this casepatterns to associate in sets with the isotopic variants are notreadily deciphered; Table 1 indicates one plausible doublet foreach isotopic variant, whereas 28 lines are left unassigned but allare associated with mode ν17 and combinations of other modesthat might arise through Fermi resonance. At about 2525 cm 1,three plausible doublets, shown in Figure 2e, are likewiseassigned to the isotopic variants but another 18 signals remainunaccounted; all are associated with mode ν16 and associatedcombinations. These three modes ν16, ν17, and ν18 belong tosymmetry class B3u. Moderately intense lines in two other setsare associated with ν9 of class B1u and ν12 of class B2u. The linesin the latter set at about 2615 cm 1, also shown in Figure 2e,are noticeably broad with widths 1.4 cm 1 at half-maximumstature to be compared with widths 0.22 cm 1 of lines near2525 cm 1; only a single but broad line is associated with aparticular isotopic variant with intervals comparable with those5565DOI: 10.1021/acs.jpca.6b05150J. Phys. Chem. A 2016, 120, 5562 5572
ArticleThe Journal of Physical Chemistry ATable 2. Wavenumbers/cm 1 of Lines in Infrared Absorption Spectra of B2D6 1:1000 in Ne at 4 K for Indicated IsotopicVariants of B, as 10B or 11B, Compared with Assigned Modes in Gaseous and Crystalline Phasesa,bB2D6 gaseousbB2D6 in .310,11B2D6 67.610,10722.7871.4modeν13ν9ν18ν14 �13 ν151404.021486.90ν5 ν15147714841424.51476.81437.51482.814451488.3ν7 ν13ν8162316391649ν3 ν917951762.21774.21784.7ν3 1980.31986.3ν16ν1ν7 1860.371997.662001.682201.791772178419771998ν8 ν11ν1 ν18A question mark (?) indicates a line or attribution uncertain because of small intensity. bFrom ref 2. cThe numbering of the mode as νn pertains toB22H6 unless wavenumbers for only 10B11B22H6 appear in that particular row of the table. dRelative statures to the line at 1195.00 cm 1 are listed inTable S8 in Supporting Information.a11in the crystalline phase.2 For the lines near 975 cm 1, shown inFigure 2a, three doublets are readily identifiable, with internalseparation 0.4 cm 1 and separations 2.5 and 2.1 cm 1between them consistent with 2.4 and 2.2 cm 1 fromcalculations and similar intervals for a crystalline sample.2Figure 2d shows signals between 1850 and 2000 cm 1 in threesets; the sets near 1855 and 1889 cm 1 are attributed todoublets, associated with modes ν5 ν15 and ν8, of 11B2H6 and10 11B BH6; corresponding sets for 10B2H6 are not readilydetectable because of small intensity, but the three linesbetween 1990 and 1998 cm 1 are appropriate as singlets of eachisotopic variant, associated with combination mode ν13 ν15. Abarely resolved line at 1993.6 cm 1 provides a hint of furtherstructure in this region but the small ratios of signal to noisepreclude definite assignments. Although lines in another sevensets are measurable, their weakness precludes positiveidentification of lines due to the minor isotopic variant; allfirm assignments appear in Table 1; other measured lines areassembled in Table S1 (Supporting Information). Any line formode ν14 about 370 cm 1 lies beyond our range of detection.For the region near 1600 cm 1, gaseous B2H6 seems to showonly one intense vibration rotational band,2 assigned to themost intense fundamental mode ν17, whereas in the spectrumof the crystalline material there likely appear four or five poorlyresolved features, depending on the crystalline phase. For oursamples of B2H6 dispersed in solid neon under conditions inwhich aggregation of diborane molecules was greatly suppressed through their effective dilution with neon, beyond thetwo triplets in Table 1 we distinguished 38 components of theabsorption between 1593 and 1608 cm 1, listed in Table S1without attribution to particular isotopic variants, as describedabove. Similarly in the region near 2520 cm 1, two tripletsassociated with mode ν12 are readily attributed to isotopiccarriers containing 11B2, 10B11B, and 10B2 but another 20components of the total absorption remain unassigned between2509 and 2542 cm 1. In the preceding work, the influence ofFermi resonance was considered qualitatively but thatinteraction fails to provide an accurate explanation of theextent or nature of our data. Because our samples of B2H6 andB2D6 have great nominal purity, it seems unlikely that other5566DOI: 10.1021/acs.jpca.6b05150J. Phys. Chem. A 2016, 120, 5562 5572
ArticleThe Journal of Physical Chemistry ATable 3. Calculated Data of Diborane(6) (Point Group D2h Vh), ΔHf 50.1 kJ mol 1, Calculated Wavenumber/cm 1andIntensity/km mol 1 (in Parentheses) of Vibrational Modes for Various Isotopic Diborane(6)1110B2H6 (D2h)mode (sym)ν1 (Ag)ν2 (Ag)ν3 (Ag)ν4 (Ag)ν5 (Au)ν6 (B1g)ν7 (B1g)ν8 (B1u)ν9 (B1u)ν10 (B2g)ν11 (B2g)ν12 (B2u)ν13 (B2u)ν14 (B2u)ν15 (B3g)ν16 (B3u)ν17 (B3u)ν18 (B3u)ν1 (Ag)ν2 (Ag)ν3 (Ag)ν4 (Ag)ν5 (Au)ν6 (B1g)ν7 (B1g)ν8 (B1u)ν9 (B1u)ν10 (B2g)ν11 (B2g)ν12 (B2u)ν13 (B2u)ν14 (B2u)ν15 (B3g)ν16 (B3u)ν17 (B3u)ν18 (B3u)calc/cm 1(int)a2524.4 (0)2094.4 (0)1159.9 (0)770.1 (0)820.5 (0)2596.2 (0)905.2 (0)1914.4 (8.80)958.5 (16.6)1784.0 (0)863.1 (0)2610.9 (185.5)917.2 (0.20)346.8 (16.4)989.6 (0)2511.3 (148.7)1645.3 (472.6)1151.0 (76.8)1834.6 (0)1486.4 (0)884.9 (0)692.6 (0)580.1 (0)1948.8 (0)722.0 (0)1429.2 (6.77)707.2 (8.58)1279.6 (0)706.1 (0)1956.6 (103.9)676.1 (0.04)244.7 (8.23)700.5 (0)1814.8 (113.5)1199.0 (267.1)852.6 (26.2)11 10B2H6 (D2h)calc/cm lc/cm 1(int)a2530.4 (0)2095.2 (0)1165.4 (0)801.4 (0)820.5 (0)2611.6 (0)918.8 (0)1925.1 (9.25)963.3 (16.7)1786.3 (0)878.1 (0)2626.3 (187.7)921.6 (0.21)346.8 (16.4)989.6 (0)2516.2 (155.7)1650.2 (479.7)1157.6 (74.3)1845.2 (0)1487.4 (0)904.0 (0)706.2 (0)580.1 (0)1970.8 (0)734.9 (0)1444.2 (7.26)712.0 (8.61)1283.6 (0)722.9 (0)1977.6 (106.1)680.7 (0.03)244.7 (8.23)700.5 (0)1822.6 (122.5)1206.0 (271.8)858.7 (24.1)B BH6 (C2v)calc/cm mode (sym)ν1 (A1)ν2 (A1)ν3 (A1)ν4 (A1)ν5 (A1)ν6 (A1)ν7 (A1)ν8 (A2)ν9 (A2)ν10 (B1)ν11 (B1)ν12 (B1)ν13 (B1)ν14 (B2)ν15 (B2)ν16 (B2)ν17 (B2)ν18 (B2)ν1 (A1)ν2 (A1)ν3 (A1)ν4 (A1)ν5 (A1)ν6 (A1)ν7 (A1)ν8 (A2)ν9 (A2)ν10 (B1)ν11 (B1)ν12 (B1)ν13 (B1)ν14 (B2)ν15 (B2)ν16 (B2)ν17 (B2)ν18 (B2)calc/cm 1(int)a2528.1 (6.12)2513.3 (146.2)2095.9 (0)1648.7 (475.0)1163.7 (7.07)1153.5 (68.1)787.0 (0.04)989.5 (0)820.8 (0)1921.2 (8.92)1786.6 (0)961.1 (16.63)870.9 (0.03)2622.0 (158.3)2600.7 (28.4)920.9 (0.18)910.5 (0.04)346.0 (16.45)1839.7 (5.90)1816.5 (112.6)1488.4 (0)1203.8 (268.6)895.8 (0.20)855.6 (24.75)700.3 (0.05)699.9 (0)580.6 (0)1438.7 (6.94)1283.1 (0)718.2 (2.15)707.7 (6.48)1972.7 (70.2)1950.0 (35.0)728.7 (0)677.5 (0.03)244.8 (8.25)calc/cm These wavenumbers/cm 1 and intensities/km mol 1 within parentheses are calculated with density functional method, B3LYP/6-311 G(d,p), inharmonic approximation and scaled by 0.967. bThese wavenumbers/cm 1 are calculated in an anharmonic approximation.aand third most intense sets are adjacent, between 1840 and2000 cm 1. Near 1850 cm 1, shown in Figure 3e, threedoublets are discernible with internal intervals 2.2 cm 1, aspresented in Table 2, although the relative statures of the linesappear not to conform to the appropriate ratios of isotopicabundances; the widths of these lines are about 0.14 cm 1. Anadditional 13 lines seem to be associated with the samevibrational mode, ν16, and possible combinations in Fermiresonance. In the other set at about 1980 cm 1, shown inFigure 3f, only two doublets are clearly discernible, as presentedin Table 2, with a hint of a third doublet for 10B2D6. The widthsof lines are at least 0.5 cm 1, larger again than lines near 1840cm 1. Unlike for B2H6, for which combination lines are readilyobservable at wavenumbers much above those associated withmode ν12, in our spectra of B2D6 the only significant linebeyond 2012 cm 1, at 2347.8 cm 1, is likely due to impurityCO2.Among the lines near 875 cm 1, shown in Figure 3b, twodoublets are clearly discernible with internal intervals 0.42 cm 1compounds present as impurities are responsible for the manyunassigned lines.Like the corresponding spectrum of B2H6 in Ne, thespectrum of B2D6 in Figure 1b has prominent absorptionlines in five sets, plus moderate absorption in lines in twofurther sets, and other weak lines in more than 10 additionalsets. Figure 3c shows that in the most intense set at about 1200cm 1 three doublets, analogous to those of B2H6 in Figure 2b,are readily attributed to the three isotopic variants of diboraned6, as presented in Table 2; the intervals within the doubletshave a mean of 2.75 0.01 cm 1, and the separations betweenthe major components of the doublets are 3.4 and 6.6 cm 1,comparable with calculated shifts 4.4 and 6.3 cm 1 in Table S4(Supporting Information). The widths of the main lines at halfmaximum stature appear to be of order 0.06 cm 1, so near thenominal spectral resolution 0.04 cm 1 as to result in distortionand saturation of intensity. Another 24 weak features areperceptible within this small region, all listed in Table S2(Supporting Information). The regions of lines in the second5567DOI: 10.1021/acs.jpca.6b05150J. Phys. Chem. A 2016, 120, 5562 5572
ArticleThe Journal of Physical Chemistry Aand separation 3.46 cm 1 between major components; anyprospective third doublet is lost in the noise level. The widthsof lines are 0.09 cm 1. For the four narrow lines near 725cm 1, shown in Figure 3a, no pattern is discernible; the mostintense line at 723.15 cm 1 is tentatively associated with 11B2D6and a weaker line at 729.64 cm 1 with 10B11BD6, both for ν9.For the lines in a weaker set near 1775 cm 1, shown in Figure3d, two doublets of internal intervals of 1.65 and 1.75 cm 1 areclearly observable with a possible major component of a thirddoublet; the intervals between major lines with smaller ratios ofsignal to noise are listed in Table 2. Figure 3d shows a similartriplet of triplets of B2D6 near 1770 cm 1, assigned tocombination mode ν3 ν18, although the intermediate tripletis masked by its proximity to more intense lines in thedominant triplet. As for B2H6, beyond two prominent sets ofisotopic triplets for B2D6 perceptible for mode ν17 another 40components of the absorption between 1194 and 1237 cm 1are distinguishable but without specific attribution, listed inTable S2 (Supporting Information). For the region at about1440 cm 1, the spectra of crystalline B2D6 seem to requireinvocation of three combination modes2, ν7 ν13, ν9 ν11, ν4 ν9, but our spectrum presents 15 lines or components of noevident pattern.To assist our understanding of these spectra, we undertookquantum-chemical calculations of the wavenumbers andintensities of both B2H6 and B2D6 in all their three isotopicvariants involving boron; within a harmonic approximation, wecalculated both the wavenumbers and intensities, whereaswithin an anharmonic approximation comprising the twolargest anharmonic contributions no calculation of intensity waspracticable. The wavenumbers from the harmonic calculationswere scaled with customary factor 0.967 to take roughly intoaccount the anharmonic effects. In Supporting Information,Tables S3 and S4 for B2H6 and B2D6 present a list of allcalculated wavenumbers and intensities resulting from thesecalculations according to anharmonic approximation, asdescribed above. Apart from the deviations, small or largerelative to the accuracy of measurement, between the harmonicand anharmonic wavenumbers, the large range of calculatedintensities is most noteworthy, excluding the zero intensity formodes inactive in infrared absorption; for instance, between theintensities of 11B2H6 for mode ν17 of symmetry class B3u and ν13of class B2u a factor 2400 is calculated. Such a range,extraordinarily large relative to spectra of comparable hydrocarbon molecules, is perceptible in the experimental spectra ofboth B2H6 and B2D6 in Figures 1 3. Regarding the intensities,the ratio of intensities of modes ν8 and ν9 of 11B2D6 is, forinstance, calculated to be about 0.5, but the observed ratioappears to be about 0.1; the trend of calculated intensities ingeneral follows qualitatively that of the experimental measurements but not quantitatively. For the isotopic variantscontaining both 10B and 11B, hence belonging to point groupC2v, some modes corresponding to symmetry class A1 arecalculated to have small intensities, although their counterpartsfor variants with either 10B2 or 11B2 are inactive in infraredabsorption; for instance, Table 3 shows that modes ν1 A1, ν5 A1,and ν15 B2 of 10B11BH6, which are calculated to have significantintensity, correlate with modes ν1, ν3 and ν6, all of symmetryclass A1g of 11B2H6, which are calculated to have zero intensity.With careful measurement of spectra and great photometricaccuracy arising from digital representation of spectra convertedfrom the directly recorded interferograms, we cope with suchlarge ranges of intensities, but the ratio of signal to noise musteventually affect adversely the detectability of the weakestfeatures when the most intense lines are maintained within arange of photometric accuracy.In Table S5 (Supporting Information), we compare fordominant isotopic variant 11B2H6 the wavenumbers calculatedin both harmonic and anharmonic models with the bestexperimental data for free molecules;3 the mean deviationbetween observed and calculated wavenumbers of fundamentalmodes is 28.8 30 cm 1 for 11B2H6 and 13.8 18.4 for11B2D6. The agreement between calculated and observedwavenumbers is clearly only moderate with the discrepanciesbeing much larger than the precision of measurement. Suchlarge and erratic differences are only roughly helpful for theassignment of vibrational modes, but the calculated shifts, aspresented in Table S3 and Table S4 (Supporting Information),between 11B2H6 or 11B2D6 and the other variants are morereliable and have been applied in some assignments in Tables 1and 2. This comparison in Table S5 is valuable and meaningfulnot only in its own right within our investigation of this stablecompound diborane(6) but also as an indication of what mightbe expected for a related transient species such as diborane(4)1for which well defined conditions of known concentration orisolation from other absorbing species is impracticable.Analysis of Ultraviolet Spectra of Diborane. Werecorded the ultraviolet absorption of diborane B2H6 underthree conditions, gaseous phase near 298 K with densityselected to maintain the absorbance within an appropriaterange for optical paths of two lengths, a pure solid film,
infrared spectra, the dissimilarity with 11B 2 H 6 is weak; few of the additional modes might have intensity comparable with the 8 modes of the latter, consistent with our calculations. Our analysis of our newly recorded spectra is assisted by the reported spectra of diborane in both gaseous and crystalline phases for both B 2 H 6 and B 2 D 6 .
The infrared and Raman spectra of 3,4,5-trimethoxybenzaldehyde (3,4,5-TMB) were reported by Gupta et al (1988). But only thirteen fundamental vibrations have been observed. In the present investigation laser Raman, infrared and Fourier's transform far infrared spectra of 3,4,5-TMB are recorded and forty four funda mentals are reported.
infrared radiation with molecular vibration gives infrared spectrum. If the average position and orientation of a molecule remains constant but the distance between the atoms in a molecule change, molecular vibrations are said to take place. A vibrational spectrum is observed experimentally as Infrared as well as Raman Spectra.
and cornetite were studied using a combination of infrared emission spectroscopy, infrared absorp-tion, and Raman spectroscopy. Infrared emission spectra of these minerals were obtained over the temperature range 100 to 1000 C. The infrared spectra of the three minerals are different, in line with differences in crystal struc-ture and .
designed for infrared spectra, JCAMP-DX is readily applicable to other types of data, e. g. , Raman, NMR, X-ray powder patterns, ultraviolet/visible, ESCA, TGA, chromatograms, etc. Future documents will give specifications for the storage of other types of data. This paper deals specifically with infrared data.
Digital Spectra and ASTRO Digital Spectra Plus mobile radios (mode ls W3, W4, W5, W7, and W9) to the component level. For the most part, the information in this manual pertains to both ASTRO Digital Spectra and ASTRO Digital Spectra Plus radios. Exceptions are clearly noted where they occur.
Reference Spectra The Infrared spectra of thousands of compounds have been determined and compiled by several di erent companies. Two of the most popular collections are the Sadtler Index of IR Spectra and the Aldrich Library of Infra-red Spectra Both collections are easily accessible in 'hard copy' form in most major university libraries.
The main peaks in the Raman and infrared spectra reflected Al-OH, Al-O and Si-O functional groups in high frequency stretching and low frequency bending modes. The Raman and infrared spectra reveals the nature of clay (kaoli-nite) associated with quartz. The infrared spectra are indicative to the weathered metamorphic origin of the silicate .
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