Diode laser spectroscopy of the nu(13) band of benzene cooled in a supersonic jet

The diode laser absorption spectrum of the nu(13) band of benzene cooled in a supersonic expansion has been recorded with the help of a multipass opti cal system built inside the vacuum chamber. Transitions from low J, K value s (0-10) are reported for the first time for this band: The observed freque ncies agree with the ones computed with previously existing spectroscopic c onstants. The rotational temperature of the expansion has been evaluated to be 8 +/- 5 K when using He as buffer gas at a stagnation pressure of 1.5 b ar. This value lowers in 1:10 mixtures of Ar:He at the same pressure. The e ffect of the carrier gas on the linewidth is also discussed. (C) 1999 Acade mic Press.