Knowledge Bank

The effect of certain external perturbations on the absorption spectrum of a molecular sample can be measured as [ A^{p}(\tilde{\nu})=\tilde{\nu}\sum_{j=0}Cj d^{j}[A^{\circ}(\tilde{\nu})/\tilde{\nu}]/d\tilde{\nu}^{j} ] where $Ap(\nu ~)$ and $A\circ (\nu ~)$ are the absorption curves with and without perturbation and the Cj’s are coefficients dependent on the nature and intensity of the perturbation. If these coefficients can be expressed in context of molecular-structure parameters then direct contact between experiment and molecular properties may be made. We shall discuss a van der Waals interaction model we are developing to account for the effect a high-pressure non-absorbing gas has on the absorption bands associated with Rydberg transitions of various molecular species. The specific system we use as an example is the first s-Rydberg transitions of methyliodide $(CH3I)$ in the presence of $SF6$.