Time-Resolved Pulsed FT-IR Emission Studies of Photochemical Reactions

Abstract

A time-resolved Fourier transform emission spectrometer, operating in the stop-scan mode, is demonstrated as an inexpensive and versatile instrument for observation of infrared vibrational chemiluminescence. The entire evolution of an emission spectrum is obtained from a single scan of the interferometer, with a spectral and temporal resolution of 2 cm⁻¹ and 10 ns, respectively. Results are presented for a number of radical-radical reactions studied by this technique, where emission from highly excited CO, HF, CO₂, and N₂O is observed. Measurements include nascent vibrational distributions, quantum yields for branching into different product channels, and bimolecular rate constants for the production and vibrational relaxation of product species. Experiments at low total pressure enable nascent vibrational and rotational distributions to be found for the HF fragment of the CO₂ laser photolysis of 1,1-chlorofluoroethylene. In addition, time-resolved spectra of HF, CO, CO₂, CF₄, and CHF₃ are demonstrated for infrared emission observed from a reactive ion plasma etching chamber.