Knowledge Bank

We have used a $1.5\mu m$ color-center laser, with the optothermal detection method, to study the vibrational predissociation in the $2\nu 1$ hands of HCN dimer and HCN-HF. For HCN dimer the complexation-induced redshift of -6.3923(5) $cm-1$ is nearly exactly equal to twice the fundamental redshift, indicating a very small (0.1%) increase in the anharmonicity of the CH stretch potential. However, the much smaller than twice the fundamental redshift (-1.2905(5) $cm-1$), observed in the overtone of HCN-HF, indicates a relatively large (1%) decrease in the anharmonicity. The linewidths of the HCN dimer spectrum are instrument limited, giving a lower limit of 11 ns to the lifetime. The upper limit is given by the $90\mu s$ time-of-flight from laser crossing to detector. In the case of HCN-HF we find linewidths broader than the 22 MHz instrumental width. The homogeneous contribution to the overall linewidth is roughly 15 MHz, which compares to a 9.9 MHz Lorentzian component that was needed to fit the fundamental transitions. Presently, efforts are underway to measure the overtone linewidths at improved resolution.""