Observation of a new electronic state of CO perturbing W 1Π(ν=1)

We observe photoabsorption of the W(1) <- X(0) band in five carbon monoxide isotopologues with a vacuum-ultraviolet Fourier-transform spectrometer and a synchrotron radiation source. We deduce transition energies, integrated cross sections, and natural linewidths of the observed rotational transitions and find a perturbation affecting these. Following a deperturbation analysis of all five isotopologues, the perturbing state is assigned to the nu = 0 level of a previously unobserved (1)Pi state predicted by ab initio calculations to occur with the correct symmetry and equilibrium internuclear distance. We label this new state E '' (1)Pi. Both of the interacting levels W(1) and E ''(0) are predissociated, leading to dramatic interference effects in their corresponding linewidths. (C) 2014 AIP Publishing LLC.