Nanosecond transient grating studies of jet-cooled NO2

We report the application of nanosecond transient grating spectroscopy to p robe the excited state level structure of NO2 near 487.9 nm. Intensity and polarization grating transients were obtained in one-color (DFWM) and two-c olor (TC-RFWM) configurations. Most grating transients exhibit pronounced b eats, arising from coherences among excited state hyperfine levels, which a re enhanced in polarization grating experiments. Analysis of these beats yi elds detailed information on the excited state hyperfine level structure at a resolution 100 times smaller than the bandwidth of the applied laser fie lds. The grating transients are compared to predictions of the grating deco mposition method (GDM) using Fourier transform analysis. (C) 1999 American Institute of Physics. [S0021-9606(99)00112-9].