Photodissociation of HN3 in the Vacuum-Ultraviolet Production and Reactivity of Electronically Excited NH

Photodissociation processes of HN₃ yielding electronically excited species have been studied in the vacuum ultraviolet. The fluorescence originating from these species has been investigated in the spectral region from 1700–6000 Å. The predominant excited species are $\mathrm{NH}{c}^1\Pi$ , $\mathrm{NH}{A}^3{\Pi }_i$ , and probably ${\mathrm{N}}_2{B}^3{\Pi }_g$ . The yield of the $\mathrm{NH}{c}^1\Pi$ production is at most 2%. The (0, 0) band is most intense among the (0, 0), (1, 0), and (0, 1) bands of the $\mathrm{NH}{c}^1{\mathrm{\Pi –a}}^1\Delta$ system observed both at the Kr and Xe lines. The intensity of the (1, 0) band is 7% of that of the (0, 0) band. Rotational levels in the (0,0) band are populated up to $\text{K\hspace{0.17em}=\hspace{0.17em}18}$ . Direct formation of the $\mathrm{NH}{A}^3{\Pi }_i$ , a spin‐forbidden process, appears to be minor. The pressure dependence of the ratio, $\mathrm{NH}{A}^3{\Pi }_i$ to $\mathrm{NH}{c}^1\Pi$ , indicates that the $\mathrm{NH}{A}^3{\Pi }_i$ may be formed largely by the reaction of electronically excited N₂, most probably ${\mathrm{N}}_2{B}^3{\Pi }_g$ , with HN₃. The absorption coefficient of HN₃ has been measured in the vacuum‐ultraviolet region in order to examine its correlation with dissociation processes. It was concluded that the $\mathrm{NH}{c}^1\Pi$ may be formed from predissociation of electronically excited HN₃ below 1450 Å, while above 1450 Å apparently from direct dissociation. The $\mathrm{NH}{c}^1\pi$ is quenched almost in every collision with H₂, CO, O₂, and NO. It was found that the main quenching process by paramagnetic gases, O₂ and NO, is the conversion of the $c^1\Pi$ to the $A^3{\Pi }_i$ . Other primary processes are discussed in conjunction with the present work.