Spectroscopic study on deuterated benzenes. I. Microwave spectra and molecular structure in the ground state

Abstract

We observed microwave absorption spectra of some deuterated benzenes and accurately determined the rotational constants of all H/D isotopomers in the ground vibrational state. Using synthetic analysis assuming that all bond angles are 120°, the mean bond lengths were obtained to be r0(C-C) = 1.3971 Å and r0(C-H) = r0(C-D) = 1.0805 Å. It has been concluded that the effect of deuterium substitution on the molecular structure is negligibly small and that the mean bond lengths of C-H and C-D are identical unlike small aliphatic hydrocarbons, in which r0(C-D) is about 5 mÅ shorter than r0(C-H). It is considered that anharmonicity is very small in the C-H stretching vibration of aromatic hydrocarbons.

Spectroscopic study on deuterated benzenes. II. High-resolution laser spectroscopy and rotational structure in the S1 state

“…The rotational constants in the ground state were accurately determined by Oldani and Bauder. 18 Although we also determined these values using the mean molecular structure, which is given in Paper I, 5 our values were almost identical to their values. In this spectral analysis, we used our values and determined the rotational constants at the 6a and 6b vibrational levels in the S 1 state by a least-squares fit using the PGOPHER program.…”

“…The mixed sample of deuterated benzenes is the same as that used in Paper I. 5 Here, we briefly describe the experimental setup because the details were described previously. 15,16 We generated a supersonic jet with He gas at the stagnation pressure of 70 atm.…”

“…[1][2][3][4] In Paper I, we showed that the benzene molecule was a planar regular hexagon (D 6h ) and the structure was not changed by deuterium substitution. 5 In the electronic excited state, the mean molecular structure is easily varied with adiabatic and non-adiabatic interactions. Highresolution spectroscopy is powerful for investigating such interactions and excited-state dynamics.…”

Spectroscopic study on deuterated benzenes. III. Vibronic structure and dynamics in the S1 state

“…The mixture sample of deuterated benzenes is the same as used in Paper I. 10 In the pure sample measurement, commercial samples of C 6 H 6 (Wako Chemical, 98%), C 6 D 6 (Wako Chemical 99.8%), and C 6 HD 5 (Aldrich, 98%) are also used without additional purification. The vapor was mixed with He gas (2 atm) and expanded into a vacuum chamber through a pulsed nozzle (automobile fuel injector) to generate a supersonic jet.…”

“…[1][2][3][4][5][6][7][8][9] The C 6 H 6 molecule is a regular hexagon in the zero-vibrational level of the S 0 state, and the molecular structure has been found to be unchanged by deuterium substitution, as shown in Paper I. 10 In the S 1 state, however, the molecular structure and potential energy surface are easily changed by various interactions among the electronic excited states. It is essential to accurately analyze the vibronic structure to elucidate the excited-state dynamics such as radiationless transition and photochemical reaction because these processes are controlled by the potential energy surface.…”