A New Method for Band Contour Analysis with Application to the Spectrum of Pyridine-4-d1

Abstract

A new method for generating band contours is described which is both rapid and accurate. One contour is generated from another using the differentials of the energy levels with respect to the rotational constants, thus avoiding the need for repeated diagonalization of the asymmetric rotor matrices.The method is applied to two C-type bands in the near ultraviolet π*–n transition of pyridine-4-d1. For the 0–0 band the following constants are obtained: A′ = 0.19843 ± 0.00008 cm−1, B′ = 0.17957 ± 0.00008 cm−1, C′ = 0.09426 ± 0.00020 cm−1, ν0 = 34 800.31 cm−1. These constants are slightly smaller than the ground state constants, indicating a very small increase in the molecular dimensions in the excited state.