Quadrupole and hexadecapole moments for molecular nitrogen

Complete fourth-order Moeller-Plesset perturbation theory (MPPT) calculations for the quadrupole (Q₂) and hexadecapole (Q₄) moments of N₂ are reported. The authors' fourth-order MPPT values are Q₂=-1.171 ea²₀ and Q₄=-5.8 ea⁴₀ at a bond length of R=2.073 42 a₀. Taking basis-set truncation and vibrational corrections into account, these values are in good agreement with experiments. Preliminary values for the longitudinal components of the quadrupole polarisability, mixed dipole-quadrupole hyperpolarisability and dipole hyperpolarisability are C_zz,zz=33.64 e²a⁴₀E^-1_h, B_zz,zz=-215 e³a⁴₀4 E^-2_h and gamma _zzzz=1173 e⁴a⁴₀E^-3_h, respectively.