Measurement of adiabatic ionization energies of the rotational isomers of n-propylbenzene and m-fluorophenol by direct VUV laser photoionization

Direct photoionization of supersonic jet-cooled n-propylbenzene and m-fluorophenol was observed using a tunable VUV laser fitted with a custom-made 4-prism wavelength separator. Distinct ionization thresholds were readily measured for the two stable rotational isomers in each case, and the adiabatic ionization energies were determined to be 70 410 cm−1 and 70 269 cm−1 for the gauche and trans forms of n-propylbenzene and 70 193 cm−1 and 70 451 cm−1 for the cis and trans isomers of m-fluorophenol, respectively. These values are in excellent agreement with literature values determined from two-color (1 + 1′) REMPI experiments and demonstrate the utility of the tunable VUV system in the study of photoionization processes in molecular beam experiments.