NEW SPECTRAL TECHNIQUES - TIME-RESOLVED FOURIER-TRANSFORM SPECTROSCOPY AND 2-COLOR LASER-INDUCED GRATING SPECTROSCOPY

Time-resolved Fourier-transform spectroscopy and two-color laser-induc ed grating spectroscopy are two new techniques recently employed in th is laboratory. We recorded emission in the near infrared region during laser photolysis of HONO2 with a step-scan Fourier-transform spectrom eter and achieved temporal resolution in the microsecond range and spe ctral resolution of 0.1 cm(-1). Rotationally resolved emission lines o f the (0,0) band of the D-2 Sigma(+) --> A (2) Sigma(+) transition of NO in the region 8900-9300 cm(-1) with irregular relative intensities were observed when an ArF excimer laser was used to photodissociate HO NO2. The spectroscopic parameters of both D 2 Sigma(+) and A (2) Sigma (+) states agree with those previously reported. When a narrow-band Ar F laser was used, selective rotational levels of the D state of NO wer e populated depending on the wavelength of the ArF laser. Our results indicate that absorption of a 193-nm photon by NO(upsilon '' = 1) is r esponsible for the observed emission. To test the technique of two-col or laser-induced glaring spectroscopy, we employed the B (IIou+)-I-3-X (1) Sigma(g)(+) system of I-2. Background-free spectra with transitio ns involving rotationally selected states were recorded. Various exper imental schemes were employed with population gratings formed in eithe r the B or X state. Signals due to different four-wave mixing schemes were distinguished by variation of relative timing between the grating beams and the probe beam.