Microwave spectra, nuclear field shift effects, geometries and hyperfine constants of bismuth mononitride, BiN, and bismuth monophosphide, BiP

The diatomic molecules BiN and BiP have been prepared using a laser ablation technique and studied by Fourier transform microwave spectroscopy in the frequency range 7-22GHz. For BiN, only the J=1-0 transition fell within this range. Transitions for the ground and first excited vibrational states have been observed for both Bi¹⁴N and Bi¹⁵N. For BiP, which has only one isotopomer, the transitions J′-J″=1-0, 2-1 and 3-2 have been observed, but only for the ground vibrational state. Hyperfine structure has been observed for both nuclei in both molecules; the ²⁰⁹Bi nuclear quadrupole coupling constants show that the electronic structures are similar for the two molecules. Improved bond lengths have been obtained for both molecules. Density functional methods have been used to estimate the electron density at the bismuth nucleus in each molecule and hence allow an estimate of the uncertainty due to field shift effects in the experimentally derived bond lengths.