Determination of the branching ratios for the reaction of hot H atoms withBrCN and ClCN

The relative rates for the reaction of translationally energetic H atoms-wi th XCN to yield HNC + X, HCN + X, and HX + CN, where X is Br or Cl, have be en determined using time- and frequency-resolved absorption spectroscopy. T he H atoms were created with an average translational energy of 92 kJ mol(- 1) by the laser photolysis of CH3SH at a wavelength of 248 nm. The measurem ents were carried out at a total pressure of several torr. The dominant cha nnel for each reaction system was the production of hydrogen isocyanide, HN C. The relative branching ratios for H + BrCN and H + ClCN were determined to be 0.85/0.13/0.017 and 0.74/0.25/0.01 for the HNC/HCN/HX + CN channels, respectively. The ratio of the total reaction cross sections, sigma (XCN), was found to be sigma (BrCN)/sigma (ClCN) = 0.84.