INTRACAVITY $Kr^{+}$ LASER EXCITATION OF $NH_{2}$ IN AN $NH_{3}/N_{2}O$ FLAME

1. R.A. Copeland, D.R. Crosley and G.P. Smith, submitted to the 20th Symp. (Int.) on Combustion, Ann Arbor, Mich., Aug 1984. $^{\ast}$ NAS-NRC POSTDOCTORAL RESEARCH ASSOCIATEAuthor Institution: Ballistic Research Laboratory$NH_{2}$ is formed in an atmospheric pressure, premixed $NH_{3}/N_{2}O$ flame. Laser fluorescence is excited over the 5400-8000 {\AA} region by placing the flame in the extended cavity of a $Kr^{+}$ ion laser operating on the 6471 {\AA} line. The fluorescence was dispersed using a lm monochromator and detected with a vidicon (OMA II). The key to the assignment of the pump transition and analysis of the fluorescence spectrum as arising from $NH_{2}$ developed from the assumption that the shortest wavelength lines $(\sim 5400 {\AA})$, which are quite strong, probably are due to emission from the laser excited vibronic level in $A^{2}A_{1}$ to the (0,0,0) level in $X^{2}B_{1}$. Analysis of lines in this region yielded a firm assignment to $(0,11,0)\to (0,0,0)$ fluorescence. Calculations show that the 6471 {\AA} pump line overlaps the $2_{02}-2_{12}$ (and, perhaps slightly, the $3_{03}-3_{13}$) rotational line of the $(0,11,0)\leftarrow (0,2,0)$ hot band. Relative fluorescence intensities from the various rotational levels in the (0,11,0) excited state support this assignment. The results indicate that rotational energy transfer in the excited state is slow in comparison to vibrational-electronic state relaxation rates in the flame, in agreement with results of Copeland, Crosley and Smith on the (0,7,0) $level^{1}$. The higher signal to noise ratio of the present experiments, however, allows observation of weak fluorescence from rotational levels other than the directly pumped level. Emissions from (0,11,0) to (0,1,0), (1,0,0), (1,1,0) and (0,4,0) also will be discussed