1985•OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information)Requires access
Study of the unimolecular decompositions of the (C/sub 3/H/sub 6/)/sup +//sub 2/ and (c-C/sub 3/H/sub 6/)/sup +//sub 2/ complexes
Wen Bih Tzeng, Y. Ôno, S. H. Linn, Coley Ng
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Abstract
The major product channels identified in the unimolecular decompositions ofC/sub 3/H/sup +//sub 6/xC/sub 3/H/sub 6/ and c-C/sub 3/H/sup +//sub 6/xc-C/sub 3/H/sub 6/ in the total energy (neutral (C/sub 3/H/sub 6/)/sub 2/ or (c-C/sub 3/H/sub 6/)/sub 2/ heat of formation plus excitation energy) range of approx.230--450 kcal/mol are C/sub 3/H/sup +//sub 7/+C/sub 3/H/sub 5/, C/sub 4/H/sup +//sub 7/+C/sub 2/H/sub 5/, C/sub 4/H/sup +//sub 8/+C/sub 2/H/sub 4/, and C/sub 5/H/sup +//sub 9/+CH/sub 3/. The measured appearance energy for C/sub 4/H/sup +//sub 7/(9.54 +- 0.04 eV) from (C/sub 3/H/sub 6/)/sub 2/ is equal to the thermochemical threshold for the formation of C/sub 4/H/sup +//sub 7/+C/sub 2/H/sub 5/ from (C/sub 3/H/sub 6/)/sub 2/, indicating that the exit potential energy barrier for the ion--molecule reaction C/sub 3/H/sup +//sub 6/+C/sub 3/H/sub 6/..-->..C/sub 4/H/sup +//sub 7/+C/sub 2/H/sub 5/ is negligible. There is evidence that the formations of C/sub 4/H/sup +//sub 7/+C/sub 2/H/sub 4/+H from (C/sub 3/H/sub 6/)/sup +//sub 2/ and (c-C/sub 3/H/sub 6/)/sup +//sub 2/ also proceed with high probabilities when they are energetically allowed. The variations of the relative abundances for C/sub 4/H/sup +//sub 7/,C/sub 4/H/sup +//sub 8/, and C/sub 5/H/sup +//sub 9/ from (C/sub 3/H/sub 6/)/sup +//sub 2/ and (c-C/sub 3/H/sub 6/)/sup +//sub 2/ as more » a function of ionizing photon energy are in qualitative agreement, suggesting that (C/sub 3/H/sub 6/)/sup +//sub 2/ and (c-C/sub 3/H/sub 6/)/sup +//sub 2/ rearrange to similar C/sub 6/H/sup +//sub 12/ isomers prior to fragmentation. The fact that C/sub 6/H/sup +//sub 11/ is found to be a primary ion from the unimolecular decomposition of (c-C/sub 3/H/sub 6/)/sup +//sub 2/ but not (C/sub 3/H/sub 6/)/sup +//sub 2/ supports the conclusion that the distribution of C/sub 6/H/sup +//sub 12/ collision complexes involved in the C/sub 3/H/sup +//sub 6/+C/sub 3/H/sub 6/ reactions is different from that in the cyclopropane ion--molecule reactions. « less