Study of Relaxation in Free Jets Using Temperature Dependence of n-Butane Mass Spectra

Abstract

Molecular beam studies of the temperature dependence of n‐butane fragmentation patterns were carried out under several conditions. Under effusive‐flow molecular‐beam formation, the temperature dependence of fragmentation to several ions from n‐butane agrees well with conventional studies. Under free‐jet expansion molecular beam formation, the fragmentation of n‐butane to several ions indicates substantial vibrational relaxation of the neutral molecule. Dilution of n‐butane with argon at room temperature gives rise to parent/fragment ion ratios that suggest that the dimer or higher clusters are contributing substantially to ion peaks normally attributed to the monomer. The unusual ions $({\mathrm{C}}_4{\mathrm{H}}_{10}{)}_n^{+}$ are readily generated. Implications of the large observed vibrational cooling and its method of detection are discussed.