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

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 6¹ levels of C₆H₆ or C₆D₆ are split into 6a¹ and 6b¹ 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