Trends in hyperfine coupling constants and electron-spin g factors for X~2sum_(g,u)~+ diatomics with 1,3,and 5 valence electrons

摘要

A comparison of electron spin resonance (ESR) parameters calcualted for X~2sum_(g,u)~+ diatomic radicals is presented,including Li_2~+,LiK~+ with one valence electron (VE);Li_2~-,LiK~-,LiBe,LiCa~+,Be_2~+,and BeCa~+ with 3 VEs;and B_2~+,BGa~+ with 5 VEs.The A_(iso) and A_(dip) constants are studied using 6-311+G(2df) basis sets and several methods (HUF,CISD,MP2,3BLYP,PW91PW91).For the s-rich radicals with 1 and 3VEs,it is found that A_9iso)A_(dip)approx=0,whereas for those of p_delta-type (such as LiB~+/LiGa~+ with 3VEs,and all presnet 5 VE radicals),the values of A_(iso) and A_(dip) are generally similar.The electron-sping g factors are calculated using perturbation expansions up to second order,a Hamiltonian based on Breit-Pauli theory,and correlated (MRCI) wave functions.All radiclas have negative values of DELTAg|| and Delta g perpendicular.The sum-over-states expansions for delta g perpendicular are dominated by the coupling with just one or two ~2II excited states.The Delta g perpendicular's of the first-row radicals Li_2~+,Li_2~-,Be_2~+,LiBe,LiB~+,and B_2~+ are about-60,-5,-120,-215,-3290,and -1300 p-m,respectivley,while for the mixed first /third-row counterparts LiK~+,LiK~-,BeCa~+,LiCa~+,LiGa~+ they are about -1200,-2480,-1000,-7840,-93700,and -800 ppm,respectivley.These results show the strong influence heavier atoms with larger spin-orbit constants ahve on delta g perpendicular of BGa~+ (when compared wit hB_2~+) is caused by the 3delta->1pi and 3delta->2pi excited states contributing positively and negativley,respectively,to this shift.Such positive contribution is at variance with the rule stating that an excitation of type delta->pi (SOMO->virtual MO) should contriubte negativley.