Line intensities in the 3-0 band of CO and dipole moment matrix elements for the CO molecule

Abstract

Line intensities in the 3-0 band of CO have been determined by the method of equivalent widths for near Doppler lines. The data were obtained with sample pressures between 4 and 40 Torr and a spectral slit width of 0.04 cm −1. The values found for the band intensity at 273°K and the linear and quadratic Herman-Wallis coefficients were 0.0135 cm −2 atm −1, 0.0118 and 1.8 × 10 −4, respectively. The expressions for the dipole moment matrix elements derived in Part I were then evaluated for the vibrational band intensities used by Young and Eachus in order to test the present theory. Good agreement with the results of Young and Eachus was obtained both for the dipole moment coefficients of CO and for the Herman-Wallis factors for the 2-0 and 3-0 bands. New dipole moment coefficients and Herman-Wallis factors based on revised 1-0, 2-0, and 3-0 band intensities at 273°K of 260, 2.06, and 0.0132 cm −2 atm −1 were then calculated by means of the present theory. The dipole moment expansion was found to be, M( r) = −0.112 + 3.10 ( r - r e ) − 0.31 ( r - r e ) 2 − 2.28 ( r - r e ) 3 where r e is the equilibrium internuclear distance in angstroms and M( r) is in Debyes. A negative sign was assigned to M 0 on the basis of the good agreement which this sign gave between observed and calculated Herman-Wallis factors. It was concluded that the general expressions obtained in Part I are of good accuracy. Previous analytic expressions obtained for the 2-0 and 3-0 bands are not as accurate primarily because they do not include quadratic and cubic dipole moment terms.