The infrared spectrum of the O center dot center dot center dot H center dot center dot center dot O fragment of H5O2+: Ab initio classical moleculardynamics and quantum 4D model calculations

The gas phase IR spectrum of the O . . .H . . .O fragment of H5O2+ and its deuterated analogue are calculated using ab initio classical molecular dyna mics based on a MP2 potential energy surface. The assignment of the bands i s made in terms of the quantum four-dimensional model calculations of anhar monic frequencies and intensities. Comparing low and high kinetic temperatu re simulations the importance of anharmonicities of the potential energy su rface for understanding the vibrational band structure is highlighted. It i s shown that any reasonable simulation of IR spectra of systems with very s trong hydrogen bonds has to account for the dipole moment function beyond t he linear approximation. (C) 2001 American Institute of Physics.