Knowledge Bank

This talk will start with a review of earlier work on the visible overtone spectrum of acetylene and its isotopomers. Discussion will focus on the overall patterns in the spectrum and the many perturbations. I will then present recent measurements of the intensity of the overtone bands of $C2H2$ and compare them with the intensities of the corresponding bands of HCN. The talk will finish with a discussion of the source of overtone intensity of the C-C-H chromphore. It is found that mechanical anharmonicity plans a much more important role than electrical anharmonicity, although a quantitative prediction of the overtone band strengths is not possible without the latter. It is found that the overtone intensities are extremely sensitive to small changes in the inner wall of the C-H potential function used, but insensitive to the outer wall. The positions of overtone bands are more sensitive to the shape of the outer wall due to its reduced slope. It is proposed that both position and intensity data be used in fitting overtone data to determine the X-H stretching potential.