Microwave spectra and structures of the NNO–HCN, 15NNO–HCN, and NNO–DCN complexes

Abstract

A total of 60 a- and b-dipole rotational transitions were measured in the 4–18 GHz range for the NNO–HCN, 15NNO–HCN, and NNO–DCN bimolecular complexes using a pulsed-beam, Fourier transform microwave spectrometer. Spectroscopic constants (A−DK), B, C, DJ, DJK, eQqaa (N of HCN), and eQqbb (N of HCN) were obtained by fitting the observed transition frequencies with a first-order quadrupole coupling interaction Hamiltonian. The structure of the complex appears to be planar with NNO and NCH nearly parallel. It can be described with the distance Rcm between the center-of-masses of the monomer subunits, the angle θ between HCN and Rcm, and the angle φ between N2O and Rcm. A least-squares fit to the nine rotational constants to obtain the structure parameters Rcm, θ, and φ, produced three local minimia for bent structures with standard deviations of <25 MHz. A Kraitchman analysis was used to determine magnitudes of principal axes coordinates for the N of HCN, and the terminal N of NNO. The best nonlinear least-squares fit result (structure I, lowest standard deviation of the fit =7.2 MHz) produced the best match to the coordinates from the Kraitchman analysis. The spectroscopic constants B, C, and eQqaa were used in a second structural analysis to determine values for Rcm, θ, and φ. These results were compared with the above coordinates. The best least-squares fit structure parameters for the vibrationally averaged structure are Rcm =3.253(4) Å, θ=89.1(5.4)°, and φ =76.4(0.4)°. Comparisons are made with other similar weakly bound complexes.