The molecular electric quadrupole moment of N2

From accurate ab initio calculations in hierarchies of basis sets and wavefunction models, the non-relativistic CCSD(T) basis set limit value of the equilibrium molecular electric quadrupole moment (Θe) of N2 has been determined. Including estimates of the small effects of relativity and correlation beyond CCSD(T), the value obtained is Θe = (−4.99±0.03)×10−40 Cm2. The corresponding rovibrationally averaged value Θ0 = (−4.93±0.03)×10−40 Cm2 is in disagreement with the recent experimental value of (−4.65±0.08)×10−40 Cm2. The latter, however, is deduced from the measured effective Θ via a correction term, whose value is questionable. Using a more accurate value for the correction term we obtain the improved experimentally based value (−5.01±0.08)×10−40 Cm2, which is in good agreement with our theoretical value.