Matrix-Isolation ESR Studies of the Various Isotopomers of the CH3Zn and ZnH Radicals: Comparisons with ab initio theoretical Calculations

The (CH3Zn)-C-12, (CH3Zn)-C-12-Zn-67, (CH3Zn)-C-13, (CH3Zn)-C-13-Zn-67, (CD3Zn)-C-13-Zn-67, and (CD3Zn)-C-13 radicals have been isolated in an inert neon matrix at 4.3 K. Their electronic structure has been probed for the first time using matrix-isolation electron spin resonance spectroscopy (MI-ESR). These radicals were generated by the reaction of laserablated zinc metal with the appropriate methyl precursor. The magnetic parameters (MHz) were determined to be g(perpendicular to) = 1.9835(4), A(perpendicular to)(H) = 14(1), A(perpendicular to)(D) = 2.2(4), A(perpendicular to)(C-13) = 166(3), and A(perpendicular to)(Zn-67) = 547(1). Estimates were derived for A(parallel to)(C-13) = 211(50) and A(parallel to)(Zn-67) = 608(5). The (ZnH)-Zn-67 radical was also generated by the reaction of laser-ablated zinc metal and hydrogen gas and studied fur the first time by MI-ESR after isolation in solid neon matrixes at 4 K. The values of the 67ZnH magnetic parameters (MHz) were determined to be g(perpendicular to) = 1.9841(3), g(parallel to) = 1.9990(5), A(perpendicular to)(H) = 505(1), A(parallel to)(H) = 503(1), A(perpendicular to)(Zn-67) = 615(1), and A(parallel to)(Zn-67) = 660(1). Earlier argon MI-ESR studies produced ZnH by conventional high-temperature methods and determined only the hydrogen hyperfine interaction and the molecular a tensor. Hartree-Fock single- and double-excitation configuration interaction (HFSDCI) and multireference single- and double-excitation configuration interaction (MRSDCI) ab initio calculations of the magnetic hyperfine interactions in the CH3Zn and ZnH radicals were performed. The A(iso)(Zn-67) and the A(dip)(Zn-67) values calculated for both radicals were within 1% of the experimental observations. However, the calculated A(iso)(C-13) values for the CH3Zn radical were low by about 50%, and the calculated A(iso)(H) value for ZnH was low by 60%. Density functional theory (DFT) yielded A(iso) values for H and C-13 in much closer agreement with experiment. A comparison is presented between the ESR results for the CH3Zn and ZnH radicals and their cadmium analogues, which have been investigated previously by MI-ESR.