Isotope dependent predissociation in the C-1 Sigma(+) ,v=0 and v=1 states of CO

Rotationally resolved spectral lines in the C-X(1,0) band of carbon monoxid e are investigated under high resolution using a coherent vacuum ultraviole t laser source, continuously tunable near 107 nm. Transition frequencies ar e determined by calibrating against a reference standard of iodine lines, r ecorded with saturation spectroscopy in the visible range, yielding an abso lute accuracy of 0.003 cm(-1) in the vacuum ultraviolet. Improved molecular constants for the excited state are clarified and Mo effects of perturbati on are found at the present level of accuracy. Line broadening measurements result in information on the excited state lifetime of the (CC)-C-1 Sigma (+),v = 1 state fur five natural isotopomers: of cal bon monoxide: tau((CO) -C-12-O-17) = 280 ps, tau((CO)-C-12-O-18) = 210 ps. tau((CO)-C-13-O-16) = 2 95 ps, tau((OO)-O-13-O-17) = 160 ps and tau((CO)-C-13-O-18) = 150 Ps. Withi n the accuracy of the present measurements: Ilo effects: of J-dependent lif etimes: were observed, for neither of the isotopomers. In addition direct t ime domain measurements: of the lifetime of the C(1)Sigma (+),v = 0 and v = 1 states of the main isotopomer are performed ill a pump-mode experiment u sing a picosecond VUV-laser, yielding tau((CO)-C-12-O-16) = 1780 ps for v = 0 and tau((CC)-C-12-C-16)) = 625 ps for v = 1. For C(1)Sigma (+), v = 0 in (CO)-C-12-O-16 and (CO)-C-13-O-16 the same lifetime is found; this lifetim e matches experimental values of the oscillator strength and hence supports previous results showing pure radiative decay ill this state; the error ma rgins however do not exclude some low level of predissociation. The measure ments indicate that the C(1)Sigma (+),v = 0 state of the (CO)-C-13-O-18 iso topomer is predissociated with an estimated yield of 17% (i.e. above the le vel of predissociation for (CO)-C-12-O-16.) From the combined data predisso ciation yields: upon excitation of the C(1)Sigma (+),v = 1 state are derive d, lying in the range 0.84-0.91. for the five less abundant isotopomers; fo r the main (CO)-C-12-O-16 isotopomer a strongly deviating predissociation y ield of 0.65 is deduced.