We present a two-dimensional collinear, adiabatic model to describe the motion of a proton in between two hydrogen molecules which adjust their elongation to trace a minimum-energy path. Together with bound states, the predissociative, vibrationally excited states involved in the electric dipole transitions are characterized. The main qualitative features of the infrared spectra of H5 + and its deuterated variant are discussed, and the effect of the temperature of the clusters is analyzed. © 2011 American Physical Society.

This work has been supported by the Consolider-Ingenio 2010 Programme CSD2009-00038 (MICINN), MICINN Grant No. FIS2010-18132, and CAM Grant No. S-2009/MAT/1467. P.B. acknowledges support from the “Fundacion Ram ´ on Areces.” The aid of COST Action ´ CM1002 (CODECS) is also appreciated.

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