Spectroscopy from first principles: a breakthrough in water line assignments

Variational calculations of the spectrum of both hot and room temperature w ater vapor have led to a major increase in the number and scope of observed vibration-rotation transitions that have full quantum number assignments. The calculations are performed using high accuracy ab initio potential ener gy surfaces. As demonstrated, it is also necessary to consider corrections due to adiabatic effects, non-adiabatic effects and the relativistic motion s of the electrons. The result of this work has been to double the number a nd energy range of the measured energy levels for water. New energy levels for the (010), (100), (020), (001), (110), (030), (011), (040), (050) and ( 060) states are presented here. Analysis of these levels and the associated transitions shows unanticipated features, including rotational difference bands, and an absence of clustering. The prospects of observing quantum mon odromy in the spectrum of water are discussed. (C) 1999 Elsevier Science B. V. All rights reserved.