High-resolution UV laser spectroscopy of jet-cooled benzene molecules: Complete rotational analysis of the S-1 <- S(o)6(o)(1)(I=+/- 1) band

The UV spectrum of the 6(0)(1) S-1 <-- S-0 vibronic transition of benzene, located at 259 nm, was recorded by means of a combination of a cw laser dou bling unit and a molecular beam apparatus. A typical linewidth of 27 MHz wa s observed, limited only by residual Doppler broadening in the supersonic b eam. Together with an estimated rotational temperature of 25 K, the rotatio nal band structure could be completely resolved, and nearly 900 transitions were assigned in the spectrum. A set of 13 molecular parameters of the vib ronic transition was simultaneously adjusted to the measured data by means of a weighted nonlinear least-squares fit procedure. The weights themselves were determined by a careful analysis of the uncertainties in the measured line frequencies. The overall rms deviation of the fit was 3.1 MHz or abou t 10% of the observed linewidth. Monte Carlo simulations were applied to th e best-fit parameter set in order to find error estimates for the single co nstants as realistic as possible. The interdependencies of the parameters w ere analyzed by means of correlation coefficients obtained from the fit out put. These statistical findings were incorporated into comparisons with res ults from other works. As far as ground state-related data are concerned ge neral agreement with IR-band investigations was found. In the electronicall y excited state, however, data are scarce and both centrifugal distortion a nd higher order Coriolis coupling parameters were determined for the first time. (C) 1999 Academic Press.