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The molecule HONS in the trans geometry has been produced by selective photolysis from HNSO and several of its isotopes in an argon matrix at 12 K. The new molecule was characterized by its IR spectrum in conjunction with a normal-coordinate analysis and ab initio calculations. With this "missing link" the HNSO transformation scheme is completed which shows that starting from HNSO in a low-temperature matrix, the molecules HOSN, HSNO, and HONS in the cis and/or trans configuration(s) can be produced by selective photolysis. According to ab initio calculations the stability in order of increasing ground-state energy is HNSO > HOSN > HSNO > HONS. In view of a selective cis ^trans isomerization cycle, the isomerization barriers were calculated for HSNO (3200 cm'1, trans -TS), HONS (4400 cm"1), and HNSO (5000 cm"1). HOSN was predicted to have no stable trans geometry. Furthermore, the lower electronically excited states of the four molecules were calculated by using the MRCI as well as the MCSCF-CI methods.

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The OH stretching wavenumbers of the cis and trans conformers of 2-halophenols were studied in the gas phase by using coherent anti-Stokes Raman spectroscopy and quantum chemical calculations. The wavenumber di †erences between the two isomers of 2-Ñuoro-, 2-chloro-and 2-bromophenol were found to be 20, 71 and 102 cm-1, respectively. These results are in good agreement with quantum chemical calculations based on the use of the density function theory. However, the calculated energy di †erences between two isomers decrease in the order Cl > Br > F. These results indicate that the vibrational wavenumber shift is not directly correlated with the strength of the intramolecular hydrogen bonding in 2-halophenols.