Hyperfine coupling constants, electron-spin g-factors and vertical spectra of the X2Σ+ radicals BeH, MgH, CaH and BZ+, AlZ+, GaZ+ (Z = H, Li, Na, K). A theoretical study

Abstract

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% p_σ(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 s_g ↔ p_u excitations.