On the molecular electric quadrupole moment of C 2H 2

Abstract

From accurate ab initio calculations the non-relativistic CCSD(T) basis set limit result of the equilibrium molecular electric quadrupole moment ( Θ e) of C 2H 2 is established. Including estimates of the small effects of relativity and correlation beyond CCSD(T), the value Θ e=(21.88±0.07)×10 −40 C m 2 is obtained. The rovibrationally averaged value is Θ=(21.48±0.12)×10 −40 C m 2. One recent experimentally deduced value of Θ is improved to include a higher-order correction term properly, and the improved value Θ=(20.9±0.8)×10 −40 C m 2 is in good agreement with the theoretical one. Another recent experimentally deduced value Θ=(20.5±0.6)×10 −40 C m 2 is slightly lower than the theoretical value. This discrepancy may originate in the rigid-rotor approximation assumed when deducing Θ from experimental data.