MEASUREMENT OF THE ELECTRIC QUADRUPOLE-MOMENTS OF CO2, CO, N-2, CL-2 AND BF3

The electric quadrupole moments of a number of molecules have been det ermined from measurement of the birefringence induced in a gas by an e lectric field gradient. The values obtained are: carbon dioxide (-14.2 7+/-0.61) x 10(-40) C m(2), carbon monoxide (-9.47+/-0.15)x 10(-40) C m(2), nitrogen (-4.65+/-0.08) x 10(-40) C m(2), chlorine (10.07+/-0.16 ) x C m(2) and boron trifluoride (12.6+/-0.7) x 10(-40) C m(2). In the calculation of the moments for carbon monoxide and boron trifluoride the small hyperpolarizability contribution was neglected in the absenc e of known values. By means of the Jones calculus a detailed analysis was made of the effects of strain birefringence in the cell windows an d imperfect orientation of polarizing components in the light path. Th is analysis led to a measurement procedure which yielded results signi ficantly different from previously reported ones obtained with essenti ally the same apparatus. The probable error in the earlier procedure i s identified.