Electronically excited states of ammonia

The photodissociation of ammonia in the absorption system. Part I. Deuterium isotope effects in the photodissociation

“…Hn the case of NH, these bands are almost completely diffuse, showing no rotational fine structure; with ND3? however, rotational lines are well resolved in the bands corresponding to c, ' = 0 or 1 (all higher members of the progression are diffuse) (5). It is apparent that the upper state is strongly predissociated, even in ND,, as the rotational lines are considerably broadened, and the quanturn yield of dissociation of unity, independent of pressure, confirms that the excited state must be very short-lived.…”

“…The dissociation products are almost exclusively (>99"; H + f NH, , and the quantum yield is close to unity and independent of pressure. The absorption spectrum shows well-resolved vibrational bands in a long progression arising from excitation of the symmetric out-of-plane bending mode (v,' ) of the planar state (4,5). Hn the case of NH, these bands are almost completely diffuse, showing no rotational fine structure; with ND3?…”

“…While it is agreed that the photolysis of arnnlonia proceeds through a predissociation, there is some uncertainty about the repujsive state involved, 2nd the precise details of the predissociation are not clear (4)(5)(6). The striking difference in the spectra of NH, and ND, suggests that ihere could be a large deuterium isotope effect in the photodissociation, and the present work was undertaken to explore this possibility, and to gain a better understandirig of the predissociation process.…”

Enrichment of nitrogen-15 by the direct laser photolysis of ammonia-d3 in the transition

“…The initial quantum yield of D, reflects the cornbodes well for the practical separation of nitrogen petition between the combination reactions [2], [ 3 ] , isotopes by the ammonia photolysis, although the and [4], and the value of about 0.25 suggests an relatively low value of r would require at least 5 almost statistical ratio of 1 : 2 : 1 for the three reacstages to achieve a useful enrichment of "N starting tions. Estimates of rates of diffusion and radical from natural abundance ND,.…”

“…As hydrazine concentration builds up further, however, reaction [8] will begin to predominate, and the yield of D, will increase again as observed. If enough N,D, were present, the yield of D, would become unity; this is stoichiornetrically iinpossible in the present system, and the final value of the D, yield when N,D, has reached its steady state will depend on a complex competition between reactions [I], [2], [3], [8]: and [9] subsequent further reactions of N,D, and other species. The same competition will also control the final quantum yield of nitrogen which in the steady state must be 113 that of D,.…”