PHOTODETACHMENT OF SINGLY SOLVATED HALIDE-IONS

Photodetachment in a Fourier transform ion cyclotron resonance (FT-ICR ) mass spectrometer was used to measure the binding energies of (CH3OH )X(-) (X = F, Cl, Br, I), (ROH)Br- (R = C2H5, i-C3H7, n-C3H7), and (CH 3CN)Br-. The methanol complexes of F- and Cl- were prepared by sequent ial ion/molecule reactions, while equilibrium solvent exchange was use d for preparation of the Br- and I- complexes. The photodetachment pro cess was observed over the wavelength range of 260-350 nm using a tuna ble dye laser with a frequency-doubling accessory. Assuming that the p hotodetachment process leads to complete dissociation to the neutral s olvent plus halogen atom, the binding energies were calculated by subt racting the known electron affinities of the halogens from the measure d photodetachment thresholds. The binding energy values obtained for ( CH3OH)F-, (CH3OH)Cl-, (CH3OH)Br-, (CH3OH)I-, (C2H5OH)Br-, (i-C3H7OH)Br -, (n-C3H7OH)Br-, and (CH3CN)Br- are 29.6, 18.7, 15.1, 14.4, 15.2, 16. 5, 16.7, and 13.4 kcal/mol, respectively. On the basis of previously p ublished theoretical potential surfaces for the neutral halogen-solven t system, the reported BEs may be high. For (CH3OH)F- and (CH3OH)Cl- t he error should be only about 0.5 kcal/mol, but it may be 1-2 kcal/mol for the Br- and I- complexes. For the alcohol/halide adducts, the ove rall observation is an increase in binding energy with decreasing RO(- ) proton affinity and increasing X(-) proton affinity.