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IR spectra of trans -diazene (diimide, HN NH) have been recorded in nitrogen and argon matrices at 20 K. An IR spectrum of a mixture of trans -diazene- d 1 and - d 2 in a nitrogen matrix has also been recorded. The method for preparing pure trans-diazene has been clarified. Revised assignments are reported for these spectra. A definitive experimental assignment of the wavenumbers of normal modes the three hydrogen/deuterium isotopologues is given. Attempts were made to photoisomierize matrix-isolated trans -diazene into the elusive cis isomer. No bands for the cis isomer were found.

trans-Hexatriene-1-(13)C(1) (tHTE-1-(13)C(1)) has been synthesized, and its high-resolution (0.0015 cm(-1)) infrared spectrum has been recorded. The rotational structure in the C-type bands for ν(26) at 1011 cm(-1) and ν(30) at 894 cm(-1) has been analyzed. To the 1458 ground state combination differences from these bands, ground state rotational constants were fitted to a Watson-type Hamiltonian to give A(0) = 0.8728202(9), B(0) = 0.0435868(4), and C(0) = 0.0415314(2) cm(-1). Upper state rotational constants for the ν(30) band were also fitted. Predictions of the ground state rotational constants for tHTE-1-(13)C(1) from a B3LYP/cc-pVTZ model with scale factors based on the normal species were in excellent agreement with observations. Similar good agreement was found between predicted and observed ground state rotational constants for the three (13)C(1) isotopologues of cis-hexatriene, as determined from microwave spectroscopy. Equilibrium rotational constants for tHTE and its three (13)C(1) isotopologues, of which two were predicted, were used to find a semiexperimental equilibrium structure for the C(6) backbone of tHTE. This structure shows increased structural effects of π-electron delocalization in comparison with butadiene and some differences from the cis isomer of HTE. Structures predicted with the MP2/cc-pVTZ model are also compared.

Assignments of the vibrational fundamentals of cis - and trans -1,3,5-hexatriene are reevaluated with new infrared and Raman spectra and with quantum chemical predictions of intensities and anharmonic frequencies. The rotational structure is analyzed in the high-resolution (0.0013–0.0018 cm −1 ) infrared spectra of three C-type bands of the trans isomer and two C-type bands of the cis isomer. The bands for the trans isomer are at 1010.96 cm −1 ( ν 14 ), 900.908 cm −1 ( ν 16 ), and 683.46 cm −1 ( ν 17 ). Ground state (GS) rotational constants have been fitted to the combined ground state combination differences (GSCDs) for the three bands of the trans isomer. The bands for the cis isomer are at 907.70 cm −1 ( ν 33 ) and 587.89 cm −1 ( ν 35 ). GS rotational constants have been fitted to the combined GSCDs for the two bands of the cis isomer and compared with those obtained from microwave spectroscopy. Small inertial defects in the GSs confirm that both molecules are planar. Upper state rotational constants were fitted for all five bands.

High-resolution (0.0013 cm −1 ) infrared spectra have been recorded for trans,trans -1,4-difluorobutadiene (ttDFBD) and cis,cis- 1,4-difluorobutadiene (ccDFBD). The rotational structure in two C-type bands ( ν 10 and ν 12 ) and one A-type band ( ν 22 ) for ttDFBD and in two C-type bands ( ν 11 and ν 12 ) for ccDFBD has been analyzed. Ground state and upper state rotational constants, except for ν 10 of ttDFBD, have been fitted. Band centers are 934.1 cm −1 ( ν 10 ), 227.985 cm −1 ( ν 12 ), and 1087.919 cm −1 ( ν 22 ) for ttDFBD. Band centers are 762.891 cm −1 ( ν 11 ) and 327.497 cm −1 ( ν 12 ) for ccDFBD. The small inertial defects in the ground state confirm that both isomers are planar. Obtaining the ground state rotational constants for the two isomers of DFBD is a first step toward determining their semi-experimental equilibrium structures.

The 2,3-13C2 isotopomer of butadiene was synthesized, and its fundamental vibrational fundamentals were assigned from a study of its infrared and Raman spectra aided with quantum chemical predictions of frequencies, intensities, and Raman depolarization ratios. For two C-type bands in the high-resolution (0.002 cm−1) infrared spectrum, the rotational structure was analyzed. These bands are for ν11 (au) at 907.17 cm−1 and for ν12 (au) at 523.37 cm−1. Ground state and upper state rotational constants were fitted to Watson-type Hamiltonians with a full quartic set of centrifugal distortion constants and two sextic ones. For the ground state, A0 = 1.3545088(7) cm−1, B0 = 0.1469404(1) cm−1, and C0 = 0.1325838(2) cm−1. The small inertial defects of butadiene and two 13C2 isotopomers, as well as for five deuterium isotopomers as previously reported, confirm the planarity of the s-trans rotamer of butadiene.

The infrared spectrum of the ν 11 ( a u ) out-of-plane CH 2 -wagging vibrational mode of the environmentally important 1,3-butadiene molecule has been investigated at sub-Doppler resolution with a CO 2 -laser/microwave-sideband spectrometer in order to fully resolve the rotational structure in a number of compact R Q-branch heads. The center frequencies of over 90 saturation Lamb dips in the 11 μm region have been measured with an estimated absolute accuracy of 200 kHz. The new data have been combined with previous Fourier transform results to refine the parameters in the molecular Hamiltonian. A value of |d μ c /d Q 11 |=0.3135 debye has been obtained for the transition dipole derivative for the ν 11 mode on the basis of ab initio calculations.

Butadiene-1- 13 C 1 was synthesized, and its high-resolution (0.002 cm −1 ) infrared spectrum was recorded for several bands in the mid-infrared region. A complete analysis of the rotational structure in the C-type band at 524.485 cm −1 for CH 2 twisting and a partial analysis of the rotational structure in the C-type bands at 900.0 and 909 cm −1 were performed. Of these latter two bands, which are of comparable intensity, the higher frequency one is largely CH 2 out-of-plane wagging and the lower frequency one is largely 13 CH 2 out-of-plane wagging. Taken together these bands correlate with one infrared-active a u fundamental and one Raman-active b g fundamental of butadiene. The ground state rotational constants are A =1.3887919 (6), B =0.1436683 (3), and C =0.1302251 (3) cm −1 , and upper state rotational constants are reported for the bands at 524.485 and 900.0 cm −1 . Medium resolution infrared and Raman spectra gave a complete assignment of the vibrational fundamentals, including 11 fundamentals observed directly for the first time.

Samples of trans , trans and cis , cis forms of butadiene-1,4- d 2 have been synthesized and found to contain useful amounts of the cis , trans species as a contaminant. Assignments of fundamental frequencies for the three isotopomers of butadiene-1,4- d 2 have been extended and improved from investigations of their Raman spectra as well as their infrared (IR) spectra. High-resolution IR spectra have been recorded for the three isotopomers, and a rotational analysis has been completed for strong bands of each species. Ground state and some upper state rotational constants have been fit. Corresponding ground state moments of inertia compare favorably with equilibrium moments of inertia obtained from B3LYP/6-311++G** theory. Two 13 C isotopomers are being prepared, and an improved structural analysis of butadiene will soon be available to assess how π-electron delocalization affects its structure.

Rotational constants for butadiene and butadiene-2,3-d2 are derived from the analysis of the rotational structure of bands in the high-resolution infrared (IR) spectra. Corresponding moments of inertia computed from three quantum chemical calculations agree acceptably with the experimental values. Evidence is growing that the CC bond lengthens some and the C–C bond shortens some in support of partial π-electron delocalization in butadiene. Refinements are made in the assignment of vibrational fundamentals of butadiene and butadiene-2,3-d2 from new observations of IR and Raman spectra of these species.

Infrared and Raman spectra are reported for cis and trans 1,2- 1 3 C 2 H 2 F 2 . Quantum chemical calculations at B3LYP and MP2 levels have been made for cis and trans 1,2-difluoroethylenes, using 6-311G** and 6-311++G** bases. The resulting harmonic force fields for each compound were scaled with nine independent factors, using frequency data corrected, where necessary, for Fermi resonances and for liquid/gas shifts. The previously accepted assignments for v 7 and v 1 2 in the trans isomer are interchanged. Several scale factors for bending motions differ markedly between the cis and trans compounds. Centrifugal distortion constants observed with significant accuracy are predicted within 6%. Harmonic contributions to the vibrational dependence of the rotational constants and perpendicular amplitudes are calculated. The C=C and C-H bonds in the cis and trans isomers are essentially identical in respect to length, force constant, and isolated CH stretching frequency. However, the C-F bond is slightly stronger in the cis compound. A revised allocation of observed infrared intensity between the overlapping trans v 7 and v 1 2 bands is needed. Directions of ∂p/∂Q for the trans B u bands are given, which differ from those reported earlier. Magnitudes and directions of the bond dipole derivatives ∂μ/∂r for the CH and CF bonds are obtained from calculated atomic polar tensors. In both cis and trans isomers, the vector ∂μ/∂r C F lies within 17° of the bond direction, but for the CH bond, ∂μ/∂r is roughly perpendicular to the CH direction.

The 13C2 and d2 isotopomers of 1,1,2,2-tetrafluoroethane (TFEA) have been synthesized. Raman spectra of these new species have been recorded, and infrared spectra of all three isotopomers, including some regions with high-resolution at −100 °C, have also been recorded. Guided by recently published calculations of frequencies and infrared intensities and the new spectra, we have revised the previous assignments of fundamentals for the two rotamers of the normal species of TFEA. Assignments of the fundamentals for both rotamers of the 13C2 and d2 isotopomers are proposed. The anti rotamer is the more abundant species in the gas phase and, to a lesser extent, in the liquid phase and the only species in the crystal phase. Thus, the assignments of the anti rotamer of all three isotopic species are complete and supported by isotope product rules, but the assignments for the gauche rotamers are incomplete. Estimates of the missing frequencies for the gauche rotamer of the normal species are supplied.

Infrared and Raman spectra were recorded for the trans,trans (EE), cis,cis (ZZ), and cis,trans (ZE) isomers of 1,4-difluorobutadiene (DFBD). From these spectra and frequencies predicted from the adiabatic connection method, which is a hybrid of Hartree−Fock and density−functional theories, complete assignments of fundamentals were made for the observable s-trans configurations. The fundamentals for the trans,trans isomer are (in cm-1): (ag) 3091, 3048, 1681, 1325, 1280, 1151, 1121, 409, 383; (au) 934, 798, 227, 154; (bg) 897, 830, 397; and (bu) 3086, 3056, 1638, 1299, 1221, 1088, 621, 133. The fundamentals for the cis,cis isomer are (in cm-1): (ag) 3118, 3088, 1676, 1410, 1248, 1134, 946, 751, 232; (au) 914, 762, 330, 78; (bg) 897, 789, 580; and (bu) 3109, 3092, 1624, 1340, 1215, 1044, 632, 165. The fundamentals for the cis,trans isomer are (in cm-1): (a‘) 3114, 3082, 3062, 3036, 1690, 1629, 1391, 1313, 1253, 1224, 1138, 1129, 1008, 706, 504, 308, 138; and (a‘ ‘) 929, 887, 824, 758, 526 (calculated), 2...

Two regions in the infrared spectrum of gaseous 1,2-difluoroethane at room temperature have been investigated at high resolution. Although bands due to the abundant gauche rotamer dominate the spectrum, a C-type band centered at 3001.89 cm-1 and a largely B-type band centered at 284.260 cm-1 have been shown to be due to the anti rotamer. From its rotational structure the C-type band is confirmed as being due to ν7, the antisymmetric CH2 stretching mode of au symmetry. The B-type band is due to ν18, which is largely the antisymmetric CF bending mode of bu symmetry. The rotational structure of the B-type band, recorded with exceptional resolution in a difficult spectral region, has been analyzed in detail. From the assignment of over 2000 lines, rotational constants have been fitted to the ground state and the upper state. The ground state constants are 1.057 385 7 (11), 0.129 390 34 (26), and 0.120 654 86 (19) cm-1 for this near-prolate symmetric top (κ = −0.9813). These rotational constants imply an incre...

Infrared and Raman spectra have been obtained in various physical states for 3,3,4,4-tetrafluorocyclobutene (TFCB) and its singly and doubly deuterated isotopic modifications. Vibrational fundamentals for TFCB are, in cm−1, (a1) 3152, 1564, 1350, 1162, 1034, 755, 500, 277; (a2)—, 957, ∼610, 348, 133; (b1) 3108, 1338, ∼1150, 1058, 730, 614, 431; (b2) 1155, 799, 366, 208. Comparably complete assignments of the fundamentals for the d1 and d2 isotopomers support these assignments. The ring puckering frequencies of 15 halogen-substituted cyclobutenes are compared. The ring puckering mode at 133 cm−1 for TFCB fits into the systematic dependence of the frequency of this mode on mass, location and extent of halogen substitution on the cyclobutene framework.

Three bands in the high-resolution infrared spectrum of trans-1,2-difluoroethylene have been examined. An A-type band at 1274 cm -1 due to in-plane CH bending, υ 10 (b u ), and a C-type band at 874 cm -1 due to out-of-plane CH bending, υ 6 (a u ) have been fully analyzed

Gas-phase infrared spectra and liquid-phase Raman spectra are presented for 1-chlorocyclobutene and 1-fluorocyclobutene. Complete assignments of vibrational fundamentals are proposed for these molecules of C s symmetry

Infrared and Raman spectra were recorded for cis-3,4-difluorocyclobutene (cDFCB) and trans-3,4-difluorocyclobutene-d4. Unscaled density functional theory (DFT) calculations of frequencies and intensities at the B3LYP/6-311++G(d,p) level supported the complete assignment of the vibrational fundamentals. The previous assignment of fundamentals of trans-3,4-difluorocyclobutene was revised. An unusual blue shift occurs for the methylenic CH-stretching frequencies of cis-3,4-difluorocyclobutene in going from the gas phase to the liquid phase. This hydrogen bond effect is related to similar observations recently reported and interpreted. The blue shift does not occur for the vinylic CH bonds of the cis isomer and does not occur for either type of CH bond in the trans isomer.

An experiment for the undergraduate physical chemistry laboratory, or an integrated analytical-physical laboratory, illustrates the application of spectroscopic selection rules for vibrational fundamentals as derived from group theory. The selection rules for the cis- and trans- isomers of 1,2-dichloroethylene are applied to assigning the vibrational fundamentals of these related but symmetrically distinct molecules. Applications of shapes of bands in gas-phase infrared spectra and of depolarization ratios of bands in liquid-phase Raman spectra are illustrated in making these assignments. The fundamental frequencies and the corresponding intensities in the infrared spectrum are compared with calculations made by DFT methods. Spectra are supplied in electronic format as part of the lab documentation.

Infrared and Raman spectra of 3-fluorocyclopropene- d 0 and - d 3 have been recorded. Complete assignments of the vibrational fundamentals for these two isotopic species are proposed. For the d 0 species the fundamentals (in cm −1 ) are: (a′) 3162, 3032, 1623, 1324, 1200, 956, 936, 660, 457; (a″) 3122, 1060, 1037, 876, 860, 446. By means of an overlay normal coordinate calculation involving the six isotopomers of 3-chlorocyclopropene as well as the two isotopomers of 3-fluorocyclopropene, empirical force constants for 3-fluorocyclopropene have been fitted. Approximate descriptions of the normal modes are proposed on the basis of the normal coordinate calculations as well as group frequency considerations. Force constants for stretching CC and CC bonds are comparable for these two halocyclopropenes.

From gas-phase and matrix-phase i.r. spectra and liquid-phase Raman spectra a complete assignment is derived for the vibrational fundamentals of 1H-trifluorocyclopropene-d0 and d1. For the undeuterated molecule the frequencies (in cm−1 and approximate characterizations of the fundamentals are: (a′) 3157 (CH stretch), 1793 (CC stretch), 1404 (CC stretch), 1160 (CC, CF stretch), 993 (CH bend), 854 (CC, CF stretch), 764 (CF2 stretch), 613 (CF bend), 500 (CF2 scissors), and 281 (CF2 rock); (a″) 1103 (CF2 stretch), 788 (CH wag), 570 (CF wag, CF2 torsion), 380 (CF wag, CF2 torsion), and 204 (CF wag, CF2 rock). All fundamentals of the undeuterated molecule and all but one of the deuterated molecule are directly observed.

Infrared and Raman spectra are reported for tetrafluorooxirane and its 18 O modification. From these spectra and previously reported microwave spectra, a complete assignment of vibrational fundamentals is obtained. For the 16 O species the frequencies in cm −1 are ( a 1 ) 1610, 1161, 792, 502, 323; ( a 2 ) 1242, 515, 234; ( b 1 ) 1286, 776, 696, 528; ( b 2 ) 1130, 558, 186. For the 18 O species they are: ( a 1 ) 1611, 1136, 789, 494, 321; ( a 2 ) 1242, 515, 234; ( b 1 ) 1284, 777, 679, 516; ( b 2 ) 1129, 539, 185. Frequency shifts with 18 O substitution show that ν 2 is symmetric CO stretching, that ν 11 and ν 12 contain antisymmetric CO stretching, and that ν 14 is flapping of the COC part with respect to the F 2 CCF 2 part. Since ν 1 is independent of 18 O substitution, this mode must be largely CC stretching mixed with symmetric CF 2 stretching. This finding corroborates a similar result for trans -2,3-difluorooxirane and negates the previous ascription of “ring breathing” to this mode.

Infrared and Raman spectra are reported for trans-2,3-difluorooxirane (difluoroethylene oxide) and its 18O and d2 isotopic modifications. Complete assignments of the vibrational fundamentals of the three species are proposed. The frequencies(in cm−)for the d0 species are:(a) 3086, 1480, 1271, 1162, 1057, 954, 511, 320; (b) 3068, 1320, 1135, 1099, 830, 578, 328. From the frequency shifts with isotopic substitution as well as group frequency considerations the normal modes are characterized approximately in terms of symmetry coordinates. CC stretching is mixed with symmetric CH bending but is largely in ν2, symmetric COC stretching is divided between ν4 and ν6, and antisymmetric COC stretching is divided between ν12, ν13, and ν14. The characterizations of the normal modes of trans-2,3-difluorooxirane have led to some revisions in the descriptions of the modes of the isoelectronic molecule, trans-1,2-difluorocyclopropane.

The i.r. spectrum of gaseous tetrafluoroethylene oxide has been investigated over the 4000-200 cm −1 region, and the fifteen vibrational fundamentals assigned. They are: ( a 1 ) 1610, 1161, 792, 501, 318; ( a 2 ) ~1300, 528, ~190; ( b 1 ) 1128, 696, 633 and 455; ( b 2 ) 1282, 557 and ~180 cm −1 . To obtain this assignment it has been necessary to assume a close parallel between the vibrational spectrum of the oxide and that of the more thoroughly studied 1,1,2,2-tetrafluoro cyclo propane.

Assignments of the twelve vibrational fundamentals for each of the three isomers of dichlorofluoroethylene and deuterodichlorofluoroethylene have been completed by means of an infrared and Raman study of CCl 2 CFD and a far-infrared study of CCl 2 CFH and of cis - and trans -CFClCClH(D). An internal coordinate representation was found which made possible transfer between the three isomers of force constants for the out-of-plane modes and thus the prediction of the elusive ν 12 fundamental for the trans isomer at about 190 cm −1 .

Infrared and Raman spectra and a complete assignment of vibrational fundamentals are presented for cis‐ and trans‐1,2‐difluoroethylenes and their deuterated modifications. For cis‐CFHCFH the fundamentals are: (a1) 3122, 1716, 1263, 1015, 237; (a2) 839, 495; (b1) 3136, 1374, 1130, 769; and (b2) 756 cm−1. For trans‐CFHCFH the fundamentals are: (ag) 3111, 1694, 1286, 1123, 548; (au) 875, 329; (bg) 788; and (bu) 3114, 1274, 1159, 341 cm−1. The near degeneracy in ν7 and ν12 of the trans isomer is shown from low‐temperature crystal and matrix studies and zero‐order normal coordinate calculations. Analysis of the rotational structure in the region of the overlapped bands proves that these fundamentals are strongly perturbed by Coriolis coupling. From the vibrational fundamentals and a previous measurement of ΔH°650, the cis isomer is shown to have 1086 cal/mole less electronic energy than the trans isomer. For the in‐plane vibrations refined Urey–Bradley potential constants are presented. These constants are obt...

Low temperature Raman spectroscopy has led to a significant revision in the assignment of the vibrational fundamentals of sulfuryl chloride fluoride (SO2FCl). The fundamentals in cm−1 are: (a′) 1230, 826, 632, 503, 422, 295; (a″) 1469, 476, 303. All are from gas-phase i.r. spectra except 295 cm−1, which is from the liquid-phase Raman spectrum. The revised assignments are consistent with the predictions of Pfeiffer's normal coordinate calculations [Z. phys. chem., Leipzig 240, 380 (1969)].

1 H -Trifluoro cyclo propene has been prepared, and twelve of its fifteen vibrational fundamentals have been assigned from the i.r. spectrum.

From the infrared spectra of gaseous carbonyl fluoride- 18 O(F 12 2 C 18 O) the six fundamental vibrational frequencies (in cm −1 ) are: (a 1 ) 1895.2 (average of Fermi resonance doublet), 947.3, 576.5; (b 1 ) 1242.3, 604.9; (b 2 ) 770.0. These unambiguous assignments are consistent with the less certain assignments for this isotopic species that Mallinson, McKean, Holloway and Oxton, Spectrochim. Acta 31A, 143 (1975) derived from an argon-matrix spectrum of 4% F 12 2 C 18 O in a mixture of four isotopomers.

Gas‐phase and matrix infrared spectra and gas‐, liquid‐, and solid‐phase Raman spectra of trans‐dimethyldiazene‐1,1,1‐d3 (CH3N=NCD3) have been recorded. A complete vibrational assignment has been secured for this molecule based on direct observation of 23 of the 24 fundamentals. Gas‐phase Raman spectra have also been obtained for trans‐dimethyldiazene‐d0 and ‐d6, which supplement published infrared and Raman spectra. On the basis of these spectra and the assignment for the d3 isotopic species revised vibrational assignments for the d0 and d6 species are proposed. The valence‐type potential function that was fitted to the d0 and d6 molecules by Pearce, Levin, and Harris has been confirmed and refined by including the frequencies of the d3 molecule in a normal coordinate calculation. This potential function has also been adapted to trans‐methyldiazene (CH3N=NH). The potential energy distributions for these two simple diazenes correlate closely for many of the normal modes. For the methyl group torsional fre...