PHOTODISSOCIATION OF C2H AT 193 NM - BRANCHING RATIOS FOR THE FORMATION OF C-2 IN THE X(1)SIGMA(+)(G), A(1)PI(U), AND B'(1)SIGMA(+)(G) STATES

The ratio of the nascent population of C-2 (X (1) Sigma(g)(+)) to C-2 (A (1) Pi(u)) to C-2 (B' (1) Sigma(g)(+)) produced from the photodisso ciation of C2H at 193 nm has been measured using laser induced fluores cence. This technique is typically used to measure rotational and vibr ational distributions in a given electronic state. Here we have extend ed the technique to measure the relative electronic distributions in t he C-2 photofragment. From the simultaneous measurement of the Mullike n (X (1) Sigma(g)(+)-D (1) Sigma(u)(+)) and Freymark (A (1) Pi(u)-E (1 ) Sigma(g)(+)) systems, the nascent population ratio of C-2 (A (1) Pi( u)) to C-2 (X (1) Sigma(g)(+)) molecules was determined. Similarly, fr om the measurement of the Deslandres-D'Azumbuja (A (1) Pi(u)-C (1) Pi( g)) and the LeBlanc (B' (1) Sigma(g)(+)-D (1) Sigma(u)(+)) systems, th e nascent population ratio of C-2 (A (1) Pi(u)) to C-2 (B' (1) Sigma(g )(+)) was determined. The overall ratio for the production of C-2 in t he X:A:B' electronic states was found to be 1:19:1.4. These results al ong with the results of high quality ab initio calculations of Cui and Morokuma (unpublished) are used to discuss the photodissociation dyna mics of C2H at 193 nm. Furthermore, these results should aid in the an alysis and modeling of cometary spectra of C-2. (C) 1997 American Inst itute of Physics. [S0021-9606(97)01147-1].