Internal Energy Distributions from Nitrogen Dioxide Fluorescence 4. Variable-Wavelength Photodissociation of ClNO2 and HONO2

published in Adounce ACS Absrrucrs, October 1, 1993. 0022-3654/93/2097-9924$04.00/0 0' 245 255 265 275 Wavelengthhm Figure 1. HONO2 absorption cross sections between 230 and 280 nm (ref 2). fragment. They infer that the NO2 fragment has about 21 000 cm-1 of internal energy after single photon dissociation but only 19 500 cm-l after VMP from the scalar properties of the OH LIF measurements. They also detected NO2* fluorescence during each process. August et a1.* used OH LIF probing to investigate the 280-nm HONO2 photodissociation. Their energy partitioning results infer that the NO2 fragments have a Gaussian distribution of internal energies with a mean value of 12 590 cm-1 and a fwhm of 6570 cm-I. Using the vector properties of their LIF results, these authors also determined that the 280-nm transition is accompanied by a pyramidal transformation of the HONO2 molecule from its planar equilibrium geometry. Bai and Sega19 have used large-scale ab initio configuration interaction calculations to determine the potential energy surfaces corresponding to the four lowest singlet states of HONO2 along the dissociation paths correlating to OH (211) and NO2 in its X 2Al and A 2B2 states. The results of this calculation are illustrated in Figure 2. One can see from the extrapolation of the potential surfaces in Figure 2 that the two lowest HONO2 surfaces correlate to N02(2A1) while the 2'A" (and the unshown 2'A') surface correlates to N02(2B2) products. These calculations verify the