First observation of the forbidden k-X transition of 13C16O

A weak rotationally resolved absorption band of (CO)-C-13-O-16 has been identified from photographic spectra at 1078 Angstrom and assigned to the forbidden transition from the X(1)Sigma(+) (v = 0) ground stare to the k(3)Pi (v = 3) valence state. It is similar in structure to the corresponding band of (CO)-C-12-O-16 but due to the fact it was photographed at a relatively low pressure only the two strongest rotational branches could be positively identified. It is the first time that the forbidden k-X transition has been observed for (CO)-C-13-O-16. The measured isotopic shift in the band origin provides independent confirmation of the new vibrational assignment of the k state by G. Berden, R. T. Jongma, D. Van der Zande, and G. Meijer (J. Chem. Phys. 107, 8303-8310 (1997)). (C) 2000 Academic Press.