Mass spectrometric direct measurements of the vibrational relaxation of hot n-butane by SF_6 and toluene in crossed molecular beams

Vibrational temperatures of hot n-butane beams before (T_(vi)) and after (T_(vf)) being deflected by nearly collinear beams of SF_6 and toluene at 300 K have been measured by mass spectrometry using low-energy electron impact ionization. For n-butane initially at 605 K a net decrease of ΔT_v = -21 ± 7 K was observed corresponding to (ΔE_v) = -230 ± 75 cm^(-1) and to a vibrational accommodation coefficient α_v = 0.18 relative to collisions in which the pool of oscillators becomes thermalized