The benzene ground state potential surface. I. Fundamental frequencies for the planar vibrations

Abstract

The accuracy of vapor phase vibrational data has been improved for all 12 deuterium-labeled benzenes and for 13C12C5H6 and 13C6H6. Many vapor phase fundamental frequencies are observed for the first time. Precise isotopic frequency/splitting patterns for ν1, ν18, and ν19 have been obtained. Isotope induced harmonic mode mixing matrices are given for all 14 labeled benzenes and used to provide detailed description of the fundamental bands observed in the spectra. These descriptions provide numerous reassignments for the fundamental bands, particularily in low symmetry deuterium benzenes. The matrices show that some skeletal modes, such as ν1, gain CH stretching character as a result of deuterium labeling, providing a rationalization for the increased anharmonicity observed in recent jet experiments for C6D6. In addition, a reassessment of Fermi resonance gives 3072.3 cm−1 for the unperturbed frequency (correction +24 cm−1) for the e1u mode ν20 in C6H6 refining the CH local mode anharmonic constant, 2xii, to 117.5 cm−1.

Complex symmeterized analysis of benzene vibrations

“…Calculations were carried out not only on the three fundamental frequencies ν 18 , ν 19 , ν 20 but also on higher E 1 u CH stretch overtone energies CH(v), at v ≤ 6, as functions of the values of the relevant harmonic force constants in benzene C 6 H 6 . The calculated vibrational energies are compared to existing experimentally measured data 13–21. The determined values of the force constants, by adjustment of the calculated to the experimentally measured vibrational energies, are displayed in Table V, together with the previously empirically determined values by Goodman et al 13 for comparison.…”

“…In our recent work 12, we studied the vibrational level structure inherent to the A 1 g block of benzene vibrations (ν 1 , ν 2 in Wilson's notation). From comparison of the ν 1 , ν 2 fundamental frequencies for four D 6 h benzene isotopomers ( C 6 H 6 , C 6 D 6 , 13 C 6 H 6 , and 13 C 6 D 6 ), calculated as functions of the relevant force constants parameters, to experimentally measured values 13–16, we have been able to determine highly accurate values for the force constants F 1,1 , F 2,2 , and F 1,2 . It must be pointed out that these calculations reproduced almost perfectly the ν 1 , ν 2 fundamental frequencies for all four benzene isotopomers 9.…”

Sub-Doppler supersonic jet spectra of the coupled 6a10and 6b10vibronic bands of the S1(1B2u) ← S0(1A1g) transition in monodeuterobenzene and their rovibrational analysis

“…Figure 1 shows the definition of the axis system used for monosubstituted benzene derivatives following the Mulliken convention [31,35]. This convention is most commonly used for electronic spectra of benzene derivatives, but differs from the one often used in infrared spectroscopy [29,36] and also the one used in [32]. In the two conventions the species B 1 and B 2 need to be interchanged.…”

Infrared–ultraviolet double resonance studies of benzene molecules in a supersonic beam

“…deuterated, C6HnD6-n) benzene molecules, which have predictably perturbed normal modes and frequencies, has also been exhaustively performed. 4,13 This has added greatly to the spectroscopic data base useful in refining force constants. High-resolution techniques have been used to measure the 3 detailed rotational structure of some vibrational bands: IR absorption14-16 and Raman17-19 studies have given accurate values of moments of inertia and vibration-rotation interaction constants.…”