SUPERSONIC FREE JET STUDY OF THE (0,0) BAND OF THE $\widetilde{A}^{1}A_{u}\leftarrow \widetilde{X}^{1}A_{g}$ OXALYL FLUORIDE SYSTEM

Oxalyl fluoride (trans-$C_{2}O_{2}F_{2}$) is prepared in the vibrationless ground state with a rotational temperature of a few degrees Kelvin by a pulsed supersonic expansion source. Laser excitation spectra are obtained by crossing the oxalyl fluoride-helium beam with a frequency-doubled, nitrogen laser-pumped tunable dye laser that has a laser bandwidth of about 1 GHz in the ultraviolet. Molecular constants obtained from a partial rotational analysis of the (0,0) vibronic band of the $\\widetilde{A}\\;^{1}A_{u}\\leftarrow \\widetilde{X}^{1} A_{g}$ system are presented. A comparison is made with previous studies of this $^system^{1,2}$