Knowledge Bank

Recent line strengths calculations for water and ozone will be discussed. Typical results are presented below for water as ratios of observed to variationally-calculated line strengths. For these (observed/variational) ratios an ab and an empirical dipole moment function were used; the observational line strengths were taken from recent $communications.2$ Dipole moment expansions were used in an internal coordinate form given by [\widetilde{M}=[M_{o}+a(\Delta R_{1} + \Delta R_{2})+b \Delta\Theta +\ldots]\hat{i}+[c_^{\prime}\Delta R_{1}-\Delta R_{2})+\ldots]\hat{j}] where $Mo$, a, b, and c, \ldots etc., are the expansion coefficients in units of Debyes, Angstroms, and radians and where $i^$ is the direction along the angle bisector and $j^$ is perpendicular to this direction. Both $i^$ and $j^$ lie in the plane of the molecule. The observational, empirical, and ab initio expansion coefficients are as follows. [FIGURE] The (observed/calculated) intensity ratios are as follows for transitions originating in the zero-point vibrational levels. The empirical expansion coefficients improve the agreement between theory and observation but there is still a rather large difference for the $\nu 1$ line of $H2O$.[FIGURE]