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

Abstract

High-resolution spectra of the S1←S0 transition in jet-cooled deuterated benzenes were observed using pulse dye amplification of single-mode laser light and mass-selective resonance enhanced multiphoton ionization (REMPI) detection. The vibrational and rotational structures were accurately analyzed for the vibronic levels in the S1 state. The degenerate 6(1) levels of C6H6 or C6D6 are split into 6a(1) and 6b(1) in many of deuterated benzenes. The rigid-rotor rotational constants were assessed and found to be slightly different between 6a and 6b because of different mean molecular structures. Their rotational levels are significantly shifted by Coriolis interactions. It was found that the Coriolis parameter proportionally changed with the number of substituted D atoms.

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

“…This 1:1 mixture was used in observing excitation spectra as shown in Papers II and III. 1,2 In this microwave experiment, to increase the intensity, the mixture of C 6 H 6 :C 6 D 6 = 1:3 was used in which the abundance ratio was 1:8:25:40:35:16:3. The sample vapor (2%) was mixed with the Ne gas and the mixed gas was expanded into a vacuum chamber from a pulsed nozzle to generate a supersonic jet.…”

“…The main objective of this study is to accurately determine the molecular structure at the zerovibrational level in the electronic ground state. In Paper II, 1 we present results of high-resolution laser spectroscopy for the S 1 1 B 2u − S 0 1 A 1g 6 1 0 (e 2g ) band and discuss the vibrational and rotational structure in the electronic excited state. In Paper III, 2 we discuss the vibronic structure in the S 1 1 B 2u state and the radiationless transition in the electronic excited state, including "channel three," which would be observed as a drastic decrease in fluorescence quantum yield for high-vibrational levels.…”

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

“…Almost all bands are combination bands with ν 6 . The 6 1 vibronic level splits into the 6a and 6b levels for several isotopomers, 17 but they are not resolved in these spectra because the laser linewidth is 0.1 cm −1 and the rotational envelope is larger than the splitting under the present jet condition (rotational temperature 20 K). Their fluorescence excitation spectra around 6 1 0 1 1 0 are shown in the upper panels of Figs.…”

“…Thus, the vibrational energy does not vary much by the deuterium substitution, although it splits into ν 6a and ν 6b for several isotopomers of lower symmetry. 17 The ν 1 (a 1g ) mode consists mainly of C−C stretching (all in-phase, which is called breathing). Deuteration reduces the vibrational energy of ν 1 more than that of ν 6 , and the decrease is approximately proportional to N D .…”

“…18 This leads to a change in the normal coordinates and the value of the Coriolis parameter ζ 6 . 17 The C−D stretching mode Q 2 of C 6 D 6 also mixes with Q H 1 , the C−C stretching mode. 19 1,3,5-C 6 H 3 D 3 is the only D 3h isotopomer.…”