Infrared spectra and relative stability of the F 3CH/NH 3 H-bonded complex in liquefied Xe

Abstract

FTIR spectra of mixtures of fluoroform (F 3CH) and ammonia (NH 3), have been studied in liquid xenon between 5400 and 500 cm −1. Spectroscopic evidence for the formation of a hydrogen bonded complex has been found and the complexation enthalpy Δ LXe H ° in the temperature interval between 173 and 215 K, was determined to be 14.4 (7) kJ mol −1. The parallel fundamentals ν 1 and ν 2 of ammonia reveal a strong narrowing effect upon complex formation, whereas the perpendicular fundamentals ν 3 and ν 4 show a modest decrease of their width. CP corrected ab initio calculations at the MP2(FULL)/6-311++G(3df,2pd) level predict a linear geometry for the complex, characterized by a small red shift of the CH stretch frequency of fluoroform. The ab initio interaction energy was found to be compatible with the isolated molecule complexation energy extrapolated from the experimental Δ LXe H ° .