Calculation of the intensities of the vibrational components of the ammonia ultra-violet absorption bands

Abstract

Abstract The intensities of the vibrational components of the A ← X and B ← X band systems of NH3 have been calculated from vibrational functions appropriate to the best one-dimensional potential curves for the inversion mode. For the A ← X system the experimental data is fitted by an expression: The Franck-Condon approximation in which the Q 2 matrix element is neglected gives a poor fit to the data. We deduce that the electronic transition moment increases as the planar molecule is bent. For the B ← X system, which is a forbidden electronic transition, the experimental data are fitted well by the matrix element <v′|Q|v″>2 which arises from the leading term in the Taylor expansion of the electronic transition moment. Using the same potential functions for ND3, and a reduced mass based on a pure bending mode, gives good agreement for the intensities of the corresponding ND3 bands. New experimental values for the extinction coefficients of the A ← X system have been obtained.