The microwave spectrum of the N 35Cl radical in the X 3Σ− state

Abstract

The microwave spectrum of the N 35Cl radical in the ground vibronic state has been observed by using a source frequency modulation spectrometer with a 3.5 m long free space absorption cell. The NCl radical was generated directly in the cell by a dc discharge in a mixture of N2 and Cl2 flowing through the cell. The electric-dipole allowed rotational transitions of N up to 4 ← 3, each being resolved into a few spin components, were observed in the frequency region 41.5–155 GHz. Each transition was found to consist of many hyperfine components. To analyze the observed spectrum, the matrix elements of magnetic hyperfine and electric quadrupole hyperfine Hamiltonians were derived for a diatomic molecule in the triplet state of which both nuclei have nonzero spins. The rotational, spin–spin interaction, and spin-rotation interaction constants were determined to be B=19 383.4655(42) MHz, λ=56 390.850(16) MHz, and γ=−208.6306(96) MHz, with three standard errors in parentheses. The hyperfine parameters b, c, and eQq for both the nitrogen and chlorine atoms were precisely determined together with the nuclear-spin rotation interaction constant for the chlorine atom. The spin density of the unpaired electrons was estimated to be 76% and 22%, respectively, on the nitrogen and chlorine atoms from the observed hyperfine coupling constants.