PHOTODISSOCIATION DYNAMICS OF $HNO_{3}$ AND $CH_{3}CFCL_{2}$ BY TIME-RESOLVED FOURIER-TRANSFORM SPECTROSCOPY

Abstract

We recorded emission in the near infrared or infrared region during laser photolysis with a step-scan Fourier-transform spectrometer; a temporal resolution in the microsecond range and spectral resolution of $0.1 cm^{-1}$ was achieved. Rotationally resolved emission lines of the (0,0) band of the $D^{2}\Sigma^{+} \rightarrow A^{2}\Sigma^{+}$ transition of NO in the range $8900-9300 cm^{-1}$ was observed during photolysis of $HNO_{3}$ with an ArF excimer laser at 193 nm. When a narrow-band (FWHM - 0.002 nm) ArF laser was used, emission from selective rotational levels of the D state of NO were observed; the selected rovibronic states depends on the wavelength of the ArF laser. Our results indicate that absorption of a 193-nm photon by NO $\bar{X}(\nu^{\prime\prime}=1)$, produced from photolysis of $HNO_{3}$, is responsible for the observed emission. Infrared emission of HCl and HF at various vibrational states were observed during photolysis of $CH_{3}CFCl_{2}$ (HCFC-141b) with an ArF laser at low pressure. Emission lines of $HF (\nu \rightarrow \nu\cdot 1)$ in the region $(3400-4200 cm^{-1})$ from vibrational states up to $\nu = 3$ preceeds that of $HCl (\\nu \rightarrow \nu\cdot 1)$ in the region $(2450-3050 cm^{-1})$ from vibrational states up to $\nu = 3$. The photodissociation dynamics will be discussed.