Nitrobenzene Detection by One-Color Laser-Photolysis/Laser-Induced Fluorescence of NO ( v” = 0–3)

Combined one-color laser-photolysis/laser-induced fluorescence methods have been applied to photodissociate nitrobenzene (NB) molecules and to detect the resulting nitric oxide (NO) photofragments. A one-color laser is used to induce photodissociation and detection of NO via the A(v‘ = 0)–X(v” = 0–4) transitions. A strongly wavelength-dependent signature is obtained due to the population of v” = 0–3 of NO. The ratios of the peak heights of the P₁₂ bandhead are (v” = 0):(v” = 1):(v” = 2):(v” = 3) = 1:0.3:0.1:0.02. A detection limit of ∼500 ppb by weight of NB in air at pressures of 10 and 100 Torr is achieved by monitoring NO X(v” = 2). This is the first attempt to use an excited NO vibrational level for NB detection, and the method can be extended to detection of other nitro compounds. It has the advantage that background of ambient ground-state NO is precluded.