VACUUM-ULTRAVIOLET LASER TIME-OF-FLIGHT MASS-SPECTROSCOPY - ION-PAIR SPECTRA OF (BRCL)-BR-79-CL-35

A newly built vacuum ultraviolet (VUV) laser/time-of-flight mass spect rometer is described, which has been used to record the first vibratio nally and rotationally resolved spectra of the E0(+) ion-pair state <- -X0(+) ground state transition of jet-cooled bromine monochloride BrCl , near 145 nm. The mass resolution of the instrument (m/Delta m approx imate to 1000) was sufficient to obtain single isotopomer data. Prelim inary results for (BrCl)-Br-79-Cl-35 are reported. Like other interhal ogens, BrCl vibronic band intensities vary widely in the VUV, presumab ly as a result of excited state perturbations. This scenario has been corroborated by the observation of an irregularly spaced vibrational p rogression, and the irregular behavior of the excited state rotational constants as a function of upsilon'.