Theoretical investigations of proton-bound cluster ions

Several proton-bound cluster ions have been studied by means of coupled clu ster calculations with large basis sets. Among these are complexes of a kry pton or xenon atom with the cations HCO+, HN2+ and HNCH+. Various spectrosc opic properties have been calculated in all cases. Effects of vibrational a nharmonicity are particularly pronounced for the intramolecular stretching vibrations of and Kr . . . HN2+ and Xe . . . HN2+. The proton stretching vi bration of (N-2)H+(N-2) is predicted around 800 cm(-1), with a large transi tion dipole moment of 1.15 D. Both(N-2)H+(N-2) and (HCN)H+ (NCH) have linea r centrosymmetric equilibrium structures. Those of (OC)H+ (CO) and (HCC-)H(CCH-) are asymmetric with barrier heights to the centrosymmetric saddle po ints of 382 and 2323 cm(-1), respectively. The dissociation energy of the a nionic complex Cl-. . . HCCH is calculated to be D-o = 3665 cm(-1), 650 cm( -1) larger than the corresponding value for Br-. . . HCCH. The complex betw een a fluoride ion and acetylene is more strongly bound and shows strongly anharmonic behaviour, similar to the bihalides FHF- or ClHCl-. Strong Fermi resonance interaction is predicted between v(3) (similar to proton stretch ) and 2v(4) (Drst overtone of intermolecular stretch).