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 (~ 7 cm-1 in FWHM~). Higher resolution measurements (~ 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 1 (~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 3 (~e'~) fundamental band, and (2) the 2 + 4 (~a2'' and e', respectively~) combination band. If this is the case (1), the 3 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 2 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 2 mode can understand about 20 % of the combination band intensity to that of the 1 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.