Isomers of CHNO in the computer, laboratory, and space
Résumé
C,H,N, and O are the four most important elements forming biomolecules and they can combine to form several isomers of the four-atom CHNO molecule, three of which (HNCO, HOCN, and HCNO) are known to exist in space and to be potentially involved in prebiotic processes in icy grain mantles. The existence of the fourth stable isomer, isofulminic acid, HONC, 84 kcal/mol above the most energetically stable isomer HNCO, has been recently shown by rotational spectroscopy supported by our coupled cluster electronic structure calculations. Isofulminic acid is a good candidate for astronomical detection with radio telescopes because it is highly polar. The abundance ratios between HONC and other isomers may provide further insight into the complex gas and surface chemistry which is thought to produce these isomers. Several important spectroscopic and dynamical issues remain unsolved for this group of molecules. As a first step towards full 6-dimensional potential surfaces for use in numerically exact rotation-vibration calculations, we have undertaken a large scale electronic structure study of electronic, spectroscopic, electric, and magnetic properties of HNCO, HOCN, HCNO, and HONC which provides results in very satisfactory agreement with the available experimentally derived values. Minimum energy paths along the angular coordinates combined with the dominant kinetic energy contributions are analysed to predict key rovibrational spectroscopic features which are clearly reminiscent of quasilinear behaviour.