Probing a strong hydrogen bond with infrared spectroscopy: Vibrational predissociation of BrHBr[sup -]·Ar.

The gas phase vibrational spectroscopy of BrHBr[sup -], a prototypical strongly hydrogen-bonded species, has been studied between 6 and 17 μm (590 and 1670 cm[sup -1]) by infrared vibrational predissociation of the BrHBr[sup -] · Ar ion. Infrared excitation was accomplished using the output of the free electron laser for infrared experiments (FELIX). Predissociation spectra were recorded by monitoring depletion of mass-selected BrHBr[sup -] · Ar ions as a function of excitation wavelength. Four prominent absorption bands are observed at 733,890, 1048, and 1201 cm[sup -1]. They are assigned to the fundamental of the hydrogenic stretching mode υ[sub 3] and a sequence of υ[sub 3] + nυ[sub 1] combinations (n = 1-3). Additional features to the blue of these bands spaced by ∼21 cm[sup -1] are attributed to combination bands involving motion of the Ar messenger atom. Differences in the relative intensities of the υ[sub 3] + nυ[sub 1] combinations bands in comparison to previous matrix experiments are rationalized on the basis of the underlying dissociation dynamics. [ABSTRACT FROM AUTHOR]