Theoretical Studies on Dications and Trications of FH, ClH, and BrH. Properties of the Bound 15Σ- States. Electron-Spin g-Factors and Fine/Hyperfine Constants of the Metastable X3Σ- States of ClH2+ and BrH2+

This theoretical study reports calculations on the fine and hyperfine structure parameters of the metastable X3Σ-(σ2π2) state of ClH2+ and BrH2+. Data on the repulsive FH2+ system are also included for comparison purposes. The hyperfine structure (hfs) coupling constants for magnetic (Aiso, Adip) and quadrupole (eQq) interactions are evaluated using B3LYP, MP4SDQ, CCSD, and QCISD methods and several basis sets. The fine structure (fs) constants (zero-field splitting λ and spin-rotation coupling γ) and electron-spin magnetic moments (g-factor) are evaluated in 2nd-order perturbation theory using multireference CI (MRCI) wave functions. Our calculations find for 35Cl of ClH2+ Aiso/Adip = 110/−86 MHz; eQq0 = −59 MHz; 2λ = 20.4 cm-1; g⊥(v = 0) = 2.02217; and γ = −0.31 cm-1 (to be compared with the available experimental Aiso/Adip= 162/-30 MHz). For 79BrH2+, the corresponding values are 300/−400 MHz; 368 MHz; 362.6 cm-1; 2.07302; and −0.98 cm-1 (experimental 2λ = 445(±80) cm-1). We find g⊥(ClH2+) to increase b...