Fluoroform

CHF₃

Deuterium

Nuclear Quadrupole Coupling Constants

in Trifluoromethane

The deuterium nqcc in trifluoromethane was measured by Kukolich, Nelson, and Ruben [1]. An equilibrium molecular structure was published by Kawashima and Cox [2] in which CH = 1.091(14) Å. Demaison and Wlodarczak [3] propose an equilibrium CH bond length of 1.085 Å. An ab initio equilibrium structure was derived by Breidung et al. [4].

The deuterium nqcc was calculated on the structure of Kawashima and Cox, on this structure but with the CH bond length of Demaison and Wlodarczak, and on the "best estimate" equilibrium structure of Breidung. These nqcc's are compared with the experimental value in Table 1. The result suggests a bond length between these two. Therefore, in Table 2, the calculated nqcc is given as a function of CH bond length. Structure parameters are given in Table 3.


Table 1. Deuterium nqcc's in CHF₃ (kHz).

	Calc. [a] CH = 1.091 Å [2]
	Calc. [b] CH = 1.085 Å [2,3]
	Calc. [c] ab initio r_e [4]

		Calc.	Expt. [1]

²H	X_zz	167.7 [a]	170.8(20)
		174.2 [b]
		173.0 [c]


Table 2. Calculated deuterium nqcc as a function of CH bond length, with CF₃ structure of Kawashima and Cox.

	r(CH) /Å		X_zz /kHz

		1.085		174.2
		1.086		173.1
		1.087		172.0
		1.088		170.9
		1.089		169.8
		1.090		168.7
		1.091		167.7

This data suggest a CH bond length of 1.088(2) Å. The uncertainty of ±0.002 Å translates to ±2.2 kHz in the nqcc. The uncertainty in the experimental nqcc is ±2.0 kHz.