Intramolecular coupling enhanced predissociation in HCCCN–HCN

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Abstract
The effect of intramolecular couplings on the dynamics of predissociation in the HCCCN–HCN complex has been studied using optothermal high resolution IR spectroscopy. Two perturbations have been observed in the ν2 band. In both cases, predissociation is enhanced by the perturbations. Because of the particular values of the rotational level spacing and the unperturbed linewidth (lifetime) of this band, perturbations are seen to affect several levels as the perturbing states tune in and out of resonance with the infrared active state. An analysis of the line intensities indicates that one of the perturbations is anharmonic in nature. A simple Fermi’s golden rule two level model for the perturbation around J=10 of the v2=1 state (the one measured with better signal to noise ratio) can not explain the experimental linewidths. Other models involving more than two levels are discussed, but firm interpretation of the data must await for a more complete theoretical analysis which goes beyond the scope of this article.