Lamb-dip millimeter-wave spectroscopy of HCP: Experimental and theoretical determination of 31P nuclear spin–rotation coupling constant and magnetic shielding

The semi-stable HCP molecule has been produced by gas phase copyrolysis of phosphine and chloroform. The three rotational transitions J = 2 ← 1, 3 ← 2, and 4 ← 3 have been recorded with sub-Doppler resolution using the Lamb-dip technique. The hyperfine structure due to the magnetic coupling between rotation and phosphorus nuclear spin has been resolved, yielding the value of the phosphorus spin–rotation constant, C(P) = 43.64 ± 0.15 kHz, from which the corresponding absolute magnetic shielding has been derived: σ(P) = 373 ± 2 ppm. Theoretical values of C(P) and σ(P) have also been calculated for HCP and NP at the CCSD(T) level of theory.