Electrical anharmonicity in hydrogen bonded systems: Complete interpretation of the IR spectra of the Cl-H→ stretching band in the gaseous (CH3)2O⋯HCl complex

Abstract

Following the previous developments to simulate the fully infrared spectra of weak hydrogen bond systems within the linear response theory, an extension of the adiabatic model is presented here. A general formulation including the electrical anharmonicities in the calculation of the damped autocorrelation function of weak H-bonds is adopted to facilitate the support of the additional properties, and thus the IR spectra of the Cl-H→ stretching band in the gaseous (CH3)2O⋯HCl complex. We have explored the origins of the broadening of the Cl-H→ stretching band. We found that the main features of the lineshape are attributed to electrical anharmonicity as a consequence of the large mixed second derivatives of the dipole moment with respect to the Cl-H→ bond and of the intermonomer elongations Cl←-H ⋯O→. In addition to providing more accurate theoretical band shapes, inclusion of the electrical anharmonicity in the present model paves the way for a more complete interpretation by generating three new Franck-Condon superposed distributions.