Microwave measurements and theoretical calculations on the structures of NNO–HCl complexes

• Published in: The Journal of chemical physics 1991-01, Vol.94 (2), p.899-907
• Main Authors: Pauley, D. J., Roehrig, M. A., Adamowicz, L., Shea, J. C., Haubrich, S. T., Kukolich, S. G.
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.459980

Pulsed-beam Fourier transform microwave spectroscopy was used to measure a and b dipole transitions for the N2O–H35Cl, N2O–H37Cl, N2O–D35Cl, and 15NNO–H35Cl van der Waals complexes. The observed transition frequencies were fit to determine the spectroscopic constants A–DK, B, C, DJ, DJK, eQqaa(Cl), and eQqbb(Cl). The structure of the complex appears to be a planar asymmetric top with a centers-of-mass separation Rc.m. ≊ 3.51 Å. The angle θ between Rc.m. and the HCl axis is approximately 110°. The angle φ between the N2O axis and Rc.m. is approximately 77°. The structure was fit using a weighted least squares fit to B and C isotopic rotational constants with Rc.m., θ, and φ as the adjustable parameters, and this procedure yielded three local minima with standard deviations less than 5 MHz. Principal axis coordinates for the Cl, H, and terminal N atoms in the complex were determined with single isotopic Kraitchman analysis to aid in the selection of the ‘‘best’’ structure. In a second structural analysis Rc.m. θ, and φ values were determined from the spectroscopic constants B, C, and eQqaa(Cl). The ‘‘best fit’’ structure parameters for N2O–HCl are Rc.m. =3.512(2) Å, θ =110(9)°, and φ = 77(2)°. Ab initio calculations of N2O–HCl structures using gaussian86 with MP2 yielded three energetically stable equilibrium conformations. One of the bound structures is very similar to the present experimental vibrationally averaged structure.