Rare Gas Effects on Hyperfine Coupling Constants of BO, AlO, and GaO

Abstract

Using density functional theory methods and large basis sets, we calculated hyperfine coupling constants (HFCCs) for the (11)B, (17)O, (27)Al, and (69)Ga nuclei of the radicals BO, AlO, and GaO (XO), embedded in 2-14 rare gas (Rg) Ne and Ar atoms. Kr atoms were included for AlO. The distance of the Rg atoms from XO was varied from 4 to 12 bohr. Matrix effects cause A(iso)(X) to increase, accompanied by decreases in A(dip)(X) and A(dip)(O), while A(iso)(O) remains close to zero. Changes are largest for AlO, slightly smaller for GaO, and very small for BO, in line with the molecular polarizabilities. Observed changes of A(iso)(X) and A(dip)(X) for BO in Ne matrixes and for AlO in Ne, Ar, and Kr matrixes are reproduced in complexes with 12 Rg atoms at distances of 5-6 bohr or 14 Rg atoms at distances of 6-7 bohr. For GaO, experimental data are available only in Ne matrixes. Theoretical results obtained for HFCCs of (17)O could not be verified due to insufficient experimental information. Estimates of HFCCs in matrixes not yet experimentally studied and for GaO in the gas phase have been made. Due to the interaction with rare gas atoms, p-spin density on the X and O atoms of XO is converted into s-spin density on X, thereby causing an increase (in magnitude) of A(iso)(X), accompanied by decreases in A(dip) of X and O. The higher polarizability of XO along the bond axis is reflected in complexes that have axial Rg atoms showing larger changes in HFCCs than comparable complexes without axial Rg atoms.

Toward Reliable Prediction of Hyperfine Coupling Constants Using Ab Initio Density Matrix Renormalization Group Method: Diatomic 2Σ and Vinyl Radicals as Test Cases

“…The experimental dielectric constants of Ne, Ar, and Kr matrices are 1.10, 1.75, and 1.85, respectively; therefore, the FC term for the Al center increases with the dielectric constant of the matrix. According to Grein’s theoretical explanation, , the large values for the FC term in Ar and Kr matrices result from the dominance of the Al 2+ O 2– configuration, which enhances the spin density at the Al center. Knight et al first used the CI method with the Dunning’s double-ζ with polarizations (DZP) basis set to evaluate the FC term for Al in AlO, and the result was in reasonable agreement with the experimental values.…”

“…However, the determination of HFCCs for the CN and AlO molecules is a challenge for the computational approaches. The difficulties are that the unrestricted treatment for CN suffers from a large degree of spin contamination, and the delicate balance between the ionic states of AlO must be handled carefully in the electronic structure calculations. − Finally, to explore the performance of present approach for HFCC prediction of multiatomic organic radicals, we evaluate the HFCCs of vinyl (C 2 H 3 ) radical. We concomitantly address the following questions of technical interest: (i) Can HFCCs be accurately described by the active-space wave function?…”

Hyperfine-Coupling Tensors from Projected Hartree–Fock Theory

“…81 The AlO radical indeed represents a multireference case, 82 and quantum-chemical calculations of its HFCs have thus proven to be nontrivial. 16,83,84 Although UHF is basically meaningless in this situation, for completeness, Table 4 does include UHF/EPR-III HFC-parameters, but no MP2 calculation was attempted. The multireference character is also reflected by the notable deviations of the CCSD(T) literature data from the gas-phase 27 Al HFC tensor.…”