Inter- and intramolecular electron transfer on formation of 15N2⋯BrCl determined from halogen nuclear quadrupole coupling in the rotational spectrum

Abstract

The ground-state rotational spectra of the four isotopomers ¹⁵N₂⋯⁷⁹Br³⁵Cl, ¹⁵N₂⋯⁸¹Br³⁵Cl, ¹⁵N₂⋯⁷⁹Br³⁷Cl and ¹⁵N₂⋯⁸¹Br³⁷Cl of a complex formed between ¹⁵N₂ and bromine monochloride were observed by pulsed-jet, Fourier-transform microwave spectroscopy. Observed spectra were characteristic of a linear or quasi-linear molecule, with Br involved in the weak interaction, and were analysed to give the rotational constant B₀, the centrifugal distortion constant D_J, the nuclear quadrupole coupling constants χ_aa(X) (X = Br or Cl) and the Br spin–rotation coupling constant M_bb(Br) for each isotopomer. Interpretation of χ_aa(X) values showed that the intermolecular electron transfer δ(N_i → Br)e on complex formation is negligible while its intramolecular counterpart δ(Br → Cl)e = 0.012(2) e is also small. The electronic redistribution is consistent with a weak interaction of N₂ and BrCl, as confirmed by the intermolecular stretching force constant k_σ = 4.40(2) N m⁻¹. Values of r(N⋯Br), δ(N_i → Br)e, δ(Br → Cl)e, and k_σ for ¹⁵N₂⋯BrCl are compared with those for HCN⋯BrCl and H₃N⋯BrCl, all of which involve weak binding of N to Br.