| Summary: | A study of the vibrational, and translational energies of the CHF (X̃1 A′) radical prepared by infrared multiphoton dissociation, IRMPD, is presented. The vibrational and rotational temperatures measured near the CO2 laser pulse peak depend on the delay, nature and pressure of the buffer gas. For pure precursor (20 mTorr) and at delays of 0.4 and 3 μs the measured rotational temperatures were 900 and 600 K, respectively. Vibrational temperatures at 3 μs delay for samples of pure precursor (20 m Torr) and of precursor with 1 Torr of Ar were 790 and 630 K. The transient migration method was applied to measure the diffusion coefficient, and hence the collisional diameter, of CHF (X̃1A′) in Ar. Attempts to measure the average translational energy of the CHF fragment by the same method at low pressures produced extremely low temperatures, and forced a re-examination of the validity of the technique. The average vibrational relaxation rate constant, as determined by the same method and confirmed by direct measurements, gives kVT < 10-15 cm3 molecule-1 s-1, while the rotational relaxation rate constant is kRT > 10-10 cm3 molecule-1 s-1. The bimolecular rate constants for removal of CHF (X̃1A′) with several alkenes are reported to be (/10-12 cm3 molecule-1 s-1): kethene = 5.4 ± 0.3; kpropene = 13.0 ± 1.0; kbutene = 9.5 ± 2.0; kisobutene = 17.0 ± 2; kbutadiene = 22.0 ± 3.0. Some of the reactions are CO2 laser fluence dependent, and, in addition, butadiene gives a considerable luminescence. A method is suggested for extrapolation of the apparent kinetic constants to zero fluence to obtain meaningful results.
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