Crossed beam studies of elementary reactions of N and C atoms and CN radicals of importance in combustion

The dynamics of some elementary reactions of N(2D), C(3P,1D) and CN(X 2&`) of importance in combustion have been investigated by using the crossed molecular beam scattering method with mass spectrometric detection. The novel capability of producing intense, continuous beams of the radical reagents by a radio-frequency discharge beam source was exploited. From angular and velocity distribution measurements obtained in the laboratory frame, primary reaction products have been identiÐed and their angular and translational energy distributions in the center-of-mass system, as well as branching ratios, have been derived. The dominant N/H exchange channel has been examined in the reaction N(2D)]CH which is found to lead to (methylenimine) and 4, H]CH2NH H]CH (methylnitrene) ; no elimination is observed. In the reaction 3N H2 N(2D)]H2O the N/H exchange channel has been found to occur via two competing pathways leading to HNO]H and HON]H, while formation of NO]H is negligible. Formation of 2 H]H (propargyl) is the dominant pathway, at low collision energy of the 2CCCH (Ec), C(3P)]C reaction, while at high formation of the less stable isomers 2H4 Ec C3H3 (cyclopropenyl and/or propyn-1-yl) also occurs ; the H elimination channel is negligible. 2 The H elimination channel has also been found to be the dominant pathway in the C(3P,1D)]CH reaction leading to isomers and, again, no elimination has 3CCH C4H3 H2 been observed to occur. In contrast, both H and H elimination, leading in comparable 2 ratio to C and respectively, have been observed in the 3H]H C3(X 1&g `)]H2(X 1&g `), reaction C(3P)]C The occurrence of the spin-forbidden molecular pathway 2H2(X 1&g `). in this reaction, never detected before, has been rationalized by invoking the occurrence of intersystem crossing between triplet and singlet manifolds of the C potential energy 3H2 surfaces. The reaction CN(X2&`)]C has been found to lead to internally excited 2H2 HCCCN (cyanoacetylene)]H. For all the reactions the dynamics have been discussed in the light of recent theoretical calculations on the relevant potential energy surfaces. Previous, lower resolution studies on C and CN reactions carried out using pulsed beams are noted. Finally, throughout the paper the relevance of these results to combustion chemistry is considered.