Influence of the geometry of a hydrogen bond on conformational stability : a theoretical and experimental study of ethyl carbamate

Spectra of ethyl carbamate (urethane) in the gas phase have been recorded in the microwave (4-20 GHz), millimeter-wave (49-118 GHz and 150-235 GHz) and mid-infrared (1000-1900 cm(-1)) regions. At the same time, high level ab initio calculations have been performed in order to both predict the experimental results and help in understanding the physical properties of the system. An extensive set of spectroscopic constants for the two most stable conformers in the gas phase, that might be useful for astrophysical databases, has been derived from the observed signals. The most stable conformer has been unambiguously identified. Then, the influence of a weak intramolecular hydrogen bond on the conformational stability has been discussed on the basis of theoretical and experimental results.