Wavelength Dependence of the Production of NO from Photodissociated C/sub 6/H/sub 5/NO/sub 2/

Upon absorption of a UV photon, nitrobenzene readily dissociates into C/sub 6/H/sub 5/, NO/sub 2/ , C/sub 6/H/sub 5/NO, O, C/sub 6/H/sub 5/O, and NO through three different channels. We have looked at the NO producing channel as a means of detecting nitro-aromatic compounds. When UV light (λ <320 nm) is used to dissociate nitrobenzene to form NO, some of the NO produced will be vibrationally hot (ν = 1 or ν = 2). We can then probe the hot NO using laser induced fluorescence (LIF). Specifically, the a tunable picosecond OPO laser system probed the A/super 2/Σ+ → X/super 2/Π(1/2,3/2) NO band system between 225-260 nm. If the A←X (0,1) or (0,2) band of NO at 236 and 246 nm respectively is excited, the LIF spectrum of hot NO will contain fluorescence blue-shifted relative to the excitation wavelength (A→X (0,0); 226 nm), which is of interest because it is the background-free region of the spectrum. In order to examine the production of hot NO, we have recorded high resolution excitation spectra of the NO resulting from photo-fragmented nitrobenzene using a two color process. In a two color process, photons of a particular energy are used to dissociate the nitrobenzene while photons of a different energy are used to probe the resultant NO. By varying the wavelength of the dissociation laser pulse, we can monitor the production of hot NO as a function of wavelength. Such monitoring is performed by comparing the relative intensity of NO emission from exciting the (0,1) versus the (0,0) bands. For all cases, we have determined the rotational and vibrational temperatures of the nascent NO.