Hyperfine coupling constants, electron-spin g-factors and vertical spectra of the X 2 Σ + radicals BeH, MgH, CaH and BZ + , AlZ + , GaZ + (Z = H, Li, Na, K). A theoretical study

Hyperfine coupling constants (hfcc), electron-spin g-factors, excitation energies (ΔE) and oscillator strengths (f-values) are calculated for the X2Σ+ (1σ22σ) radicals YH (Y = Be, Mg, Ca) and BZ+, AlZ+, GaZ+ (Z = H, Li, Na, K). Single reference ab initio and density functional theory methods are used for the hfcc's, and multireference configuration interaction wavefunctions for ΔE's, f-values and g-shifts. In XZ+ (X = B to Ga; Z = Li to K), the 2σ unpaired electron is 60–90% pσ(X), resulting in |A⊥| being one order of magnitude larger than |A‖|. The Δg⊥'s are relatively large for just 3 valence electrons, from −3300 to −6100 ppm for BZ+, −14 100 to −29 600 ppm for AlZ+, and −93 700 to −198 300 ppm for GaZ+. Such large Δg⊥(XZ+)'s relate to the strong coupling between the close-lying X2Σ+ and 12Π(2σ → 1π) states, which results from the splitting of the 2P(s2p) state of X due to its interaction with Z+. ESR spectra are not available for any of the XZ+'s. Calculation on the hydrides YH/XH+ reproduce well the experimental hfcc's and g factors, except for AlH+, which appears to be strongly perturbed in Ar matrices. Several transitions X2Σ+ → n2Σ+ and X2Σ+ → n2Π in XZ+ have large oscillator strengths, mainly caused by intramolecular charge-transfer processes X ↔ Z and atomic-like sg ↔ pu excitations.