MASARU FUKUSHIMA AND TAKASHI ISHIWATA, Faculty of Information Sciences, Hiroshima City University, Asa-Minami, Hiroshima 731-3194, Japan.

We have generated NO3 in supersonic free jet expansions and observed laser induced fluorescence (~LIF~) of the B 2E' -- X 2A2' transition. We have measured LIF excitation spectra and dispersed fluorescence (~DF~) spectra from the single vibronic levels (~SVL's~) of the B 2E' state of 14NO3 and 15NO3. The vibrational structure of the X 2A2' state has been analyzed by comparing the vibrational structures of the DF spectra of the two isotopomers. The 1,053 cm-1 band of 14NO3 is observed as two bands at 1,039 and 1,053 cm-1 with an intensity ratio of 4 : 5, respectively, for 15NO3, which are observed in the DF spectra with our standard resolution (~ sim 7 cm-1 in FWHM~). Higher resolution measurements (~ sim 2 cm-1 in FWHM~) of the DF spectra show that the 1,053 cm-1 band of 14NO3 is also observed as two bands at 1,051 and 1,056 cm-1 with an intensity ratio of 5 : 3, respectively. The 1,051 cm-1 band is attributed to be the nu1 (~a1'~) fundamental, because of its little isotope shift. There are two possibilities for another band, the band at 1,056 and 1,038 cm-1 for 14NO3 and 15NO3, respectively; (1) the nu3 (~e'~) fundamental band, and (2) the nu2 + nu4 (~a2'' and e', respectively~) combination band. If this is the case (1), the nu3 band should be observed in IR spectrum, but it has yet to be observed. If (2), the intensity must be stolen from the B 2E' -- A 2E'' transition through the nu2 mode, the considerable transition moment of which has been predicted. A simple consideration for the vibronic coupling between the A 2E'' and X 2A2' states through the nu2 mode can understand about 20 % of the combination band intensity to that of the nu1 fundamental. The higher resolution measurements of the DF spectra also show that the 1,499 cm-1 band of 14NO3 is much stronger than the 1,492 cm-1 band in the electronic spectrum, while the latter is the strongest band in the IR absorption spectrum.