Photodetachment of Singly Solvated Halide Ions

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 101; no. 13; pp. 2371 - 2378
• Main Authors: Yang, Yarjing, Linnert, Harrald V, Riveros, Jose M, Williams, Kathryn R, Eyler, John R
• Format: Journal Article
• Language: English
• Published: American Chemical Society 27-03-1997
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp960451z

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 (CH3CN)Br-. The methanol complexes of F- and Cl- were prepared by sequential ion/molecule reactions, while equilibrium solvent exchange was used for preparation of the Br- and I- complexes. The photodetachment process was observed over the wavelength range of 260−350 nm using a tunable dye laser with a frequency-doubling accessory. Assuming that the photodetachment process leads to complete dissociation to the neutral solvent plus halogen atom, the binding energies were calculated by subtracting the known electron affinities of the halogens from the measured 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 published theoretical potential surfaces for the neutral halogen−solvent system, the reported BEs may be high. For (CH3OH)F- and (CH3OH)Cl- the 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 overall observation is an increase in binding energy with decreasing RO- proton affinity and increasing X- proton affinity.