Measurement of the electric quadrupole moments of CO₂, CO and N₂

Abstract

Values for the traceless electric quadrupole moments of carbon dioxide (-13·4 ± 0·4 × 10-40 C m2), carbon monoxide (-8·58 ± 0·35 × 10-40 C m2) and nitrogen (-4·72 ± 0·26 × 10-40 C m2) are deduced from measurements of the linear optical birefringence induced in the gases by an electric field gradient. It is shown that in an optical nulling procedure, in the presence of strain in the quadrupole cell windows, the signal due to this induced birefringence need not be equal to a superimposed Kerr or Faraday nulling signal which gives zero output on a phase-sensitive detector. A procedure to find a true null is described, as are details of the apparatus which has been computer-automated on an IEEE interface bus to facilitate bulk handling of data.