Determination of Molecular Quadrupole Moment of Boron Trichloride by Microwave Spectroscopy

Abstract

The foreign-gas broadening parameter for fluoroform molecules interacting with nonpolar BCl3 molecule as perturber has been measured and the collision cross section has been determined. The results are pressure broadening coefficient Cw = (43 ± 1) [kHz/Pa] for J = 1 ← 0 rotational transition of CHF3 molecule in mixture with BCl3 gas, and collision cross section σexp = 294.0 [Å2]. Experimental linewidth parameter is interpreted using Anderson–Tsao–Curnutte as well as Murphy–Boggs theories for the mixed- interaction case. From this analysis a value of molecular quadrupole moment Q = (4.1 ± 0.2) [DÅ2] of boron trichloride molecule has been obtained.

A computational study of some electric and magnetic properties of gaseous BF3 and BCl3

“…12 However, Ritchie has raised objections to the assumptions made in that work, 13 arguing that the absorber-perturber collision cross section is not proportional to ͑⌰ 2 M͒ 1/3 where M is the reduced mass of the absorber-perturber collision pair, and that the observed spectral broadening cannot be interpreted solely on the basis of dipole-quadrupole interactions. The first assumption relied on old ⌰ values, for which Ritchie has shown that, when more recent and reliable values are used, the assumed proportionality is qualitatively and quantitatively incorrect.…”

“…u. 12 However, questions regarding this work have been raised, 13 highlighting deficiencies in the experimental technique as well as limitations in the approximations made by Gierszal et al The experimentally derived value assumed both a vanishing octupole moment of BCl 3 and a vanishing quadrupole moment of CHF 3 , neither of which are valid assumptions. 23 Clearly, the definitive value of this property has yet to be established.…”

“…9,12,13,24 The calculated and experimental quadrupole moments are listed in Table III, with only the daug-cc -pVXZ results tabulated. Concerning the calculated results, several points are worth making.…”

“…[4][5][6][7][8] The electronic charge structure of these simple molecules has been the subject of recent experimental studies, typically from linear birefringence measurements. [9][10][11][12][13][14] A linear birefringence is the difference in the refractive index along two axes perpendicular to each other and to the direction of propagation of linearly polarized light traversing a sample. It is usually induced by applying static electric and/or magnetic fields with components perpendicular to the direction of propagation.…”

“…u.͒. 9,12 Recently, the accurate determination of the quadrupole moment of BCl 3 has been debated. Gierszal et al reported measurements from a foreign-gas microwave pressure broadening study, yielding a value of 1.52± 0.07 a .…”