THE LOWEST VIBRATIONAL STATES OF UREA FROM THE ROTATIONAL SPECTRUM

The broadband 207-500 GHz spectrum of urea recorded in Dayton has signal to noise sufficient for assignment of rotational transitions in excited vibrational states up to at least 500 cm−1. In addition to the previously reported analysis of the ground and the lowest excited state we have been able to assign transitions in at least five other excited vibrational states. Strongly perturbed transitions in a close doublet of such states have been fitted to within experimental accuracy with a coupled fit and a splitting in the region of 1 cm−1. These assignments combined with vibrational energy estimates from relative intensity measurements allow for empirical discrimination between different models for the energy level manifestation of the large amplitude motions in urea.