SPECTROSCOPY AND PHOTOCHEMISTRY OF THE C-3-CENTER-DOT-H2O COMPLEX IN ARGON MATRICES

The C-3 . H2O complex has been formed in argon matrices and studied vi a FTIR spectroscopy. Five vibrational bands due to the complex have be en identified and compared with the results from ab initio calculation s (HF/6-31G level) and normal coordinate force constant adjustment ca lculations. Eight isotopomeric peaks resulting from C-12/C-13 substitu tion art observed for the asymmetric CC stretching mode at 2052 cm(-1) and lead to the conclusion that the geometry of the complex is planar and asymmetric. Photolysis of the complex at 405.4 nm results in the appearance of two intermediates, transoid and cisoid rotamers of 3-hyd roxypropadienylidene (HPD), and two stable molecules, propynal and C3O . The latter two have been observed previously in interstellar space. The existence of the intermediates was established by comparison with ab initio theoretical calculations of the vibrational frequencies and intensities, C-12/C-13 isotopic studies, and photolytic behavior. Phot olysis of the cisoid rotamer produces the transoid rotamer, with spont aneous reversion in the dark. The temperature dependence of the kineti c behavior of the dark interconversion process yields a very low activ ation energy. Ab initio theory predicts a much different value, leadin g to the suggestion that the solid-state rotamerization process may oc cur via hydrogen tunneling. The implications of this finding for the p roduction of molecules of astrophysical importance on dust particles i n the interstellar medium are discussed.