The ultraviolet photochemistry of phenylacetylene and the enthalpy of formation of 1,3,5-hexatriyne

O Sorkhabi; F Qi; A H Rizvi; A G Suits

doi:10.1021/ja0017312

The ultraviolet photochemistry of phenylacetylene and the enthalpy of formation of 1,3,5-hexatriyne

J Am Chem Soc. 2001 Jan 31;123(4):671-6. doi: 10.1021/ja0017312.

Authors

O Sorkhabi¹, F Qi, A H Rizvi, A G Suits

Affiliation

¹ Chemical Sciences Division, Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.

PMID: 11456579
DOI: 10.1021/ja0017312

Abstract

The ultraviolet photochemistry of phenylacetylene was studied in a molecular beam at 193 nm. The only primary photofragments observed were HCCH (acetylene) and C(6)H(4). Some of the C(6)H(4) molecules were found to decompose to 1,3,5-hexatriyne and molecular hydrogen. An enthalpy of formation of DeltaH(f) < or = 160 +/- 4 kcal mol(-1) was determined for 1,3,5-hexatriyne from the energetic threshold for this process. This experimentally determined value agrees well with our ab initio calculations performed at the G2 level of theory. Angular distribution measurements for the HCCH + C(6)H(4) channel yielded an isotropic distribution and were attributed to a long-lived intermediate and ground-state dissociation. An exhaustive search yielded no evidence for the phenyl + ethynyl or the atomic hydrogen elimination channels even though these were observed in the pyrolytic studies of phenylacetylene [Hofmann, J.; Zimmermann, G.; Guthier, K.; Hebgen, P.; Homann, K. H. Liebigs Ann. 1995, 631, 1995. Guthier, K.; Hebgen, P.; Hofmann, K. H.; Zimmermann, G. Liebigs Ann. 1995, 637, 1995].