ON THE ELECTRIC PROPERTIES OF BR-2

Electric multipole moments and polarizabilities for Br-2 are obtained from finite field self-consistent field (SCF), many-body perturbation theory and coupled cluster calculations with large gaussian-type basis sets. At the MP2 level of theory the bond length dependence of the me an and the anisotropy of the dipole polarizability (alpha(alpha,beta)/ e(2)a(0)(2)E(h)(-1)) around the equilibrium bond length of R-e = 2.281 05 Angstrom is adequately described by alpha(R)/e(2)a(0)(2)E(h)(-1) = 44.85 + 8.74 (R - R-e)/a(0) + 1.30[(R - R-e)/a(0)](2) -1.61[(R - R-e) /a(0)](3), Delta alpha(R)/e(2)a(0)(2)E(h)(-1) = 25.30 + 14.86(R - R-e) /a(0) + 4.32[(R - R-e)/a(0)](2) - 3.13[(R - R-e)/a(0)](3). A very larg e [18s15p12d6f] basis set consisting of 330 basis functions yields SCF values alpha = 44.10 and Delta alpha = 28.31 e(2)a(0)(2)E(h)(-1). Add ing electron correlation corrections obtained at the CCSD(T) level of theory and vibrational corrections obtained at the MP2 level, the mean dipole polarizability at the ground vibrational state is estimated at alpha = 44.74 (to be compared with the experimental value of 45.0) an d the anisotropy at Delta alpha = 25.39 e(2)a(0)(2)E(h)(-1). At the MP 2 level the mean second dipole hyperpolarizability gamma/e(4)a(0)(4)E( h)(-3) varies around R-e as 10(3) gamma(R) = 10.2 + 0.6(R - R-e)/a(0) + 5.3[(R - R-e)/a(0)](2) + 24[(R - R-e)a(0)](3) + 2.6[(R - R-e)/a(0)]( 4). SCF, MP2 and CCSD(T) results are combined to give as final theoret ical prediction the estimate of gamma = (1.02 +/- 1.0) x 10(3) e(4)a(0 )(4)E(h)(-3).