Trends in EPR g-tensors and hyperfine coupling constants of the isomer pairs HCO/COH, HCS/CSH, HSiO/SiOH and HSiS/SiSH

Abstract

Abstract For the isomer pairs HCO/COH, HCS/CSH, HSiO/SiOH and HSiS/SiSH (HXY/XYH), electron-spin g -tensors and hyperfine coupling constants are calculated. Comparison is made with experimental results for HCO and HSiO, obtained from EPR studies, and with g -shifts (Δ g = g − g e ) calculated via Curl’s equation from spin–rotation coupling constants for HCO, CSH, HSiO and HSiS. For HCO, the large component of the g -shift, Δ g yy ( y is along XY), is calculated to be −7885 ppm, compared with an EPR value of −7500 ppm, and a Curl’s value of −7975 ppm. For HSiO, the corresponding numbers are (in ppm) −8685, −5100 and −7375. Hyperfine coupling constants (HFCCs) are in good agreement with available experimental data. Interesting trends have been established and explained. The y -component of the g -shift is smaller for HXY than for XYH, except for HCS. The isotropic HFCCs have the opposite ordering. They are larger for HXY than for XYH, except for HCS. For the heavy atoms ( 13 C, 29 Si, 17 O, 33 S), A iso (X) is always larger for HXY than for XYH, and A dip (X) always smaller for HXY than for XYH, indicating that the atom bonded to hydrogen receives s-spin density at the expense of p-spin density.