Hydrogen-Bonded Complexes of HPN• and HNP• Radicals with Carbon Monoxide.

ABSTRACT

Phosphorus mononitride (PN) is a carrier of phosphorus in the interstellar medium. As the simplest derivatives of PN, the radical species HPN• and HNP• have remained elusive. Herein, we report the generation, characterization, and photochemistry of HPN• and HNP• in N2-matrix at 3 K. Specifically, HPN• was formed as a weakly bonded complex with CO in the matrix by 254 nm photolysis of the novel phosphinyl radical HPNCO•. The •NPH-CO complex is extremely unstable, as it undergoes spontaneous isomerization to the lower-energy isomer •PNH-CO through fast quantum mechanical tunneling (QMT) with a half-life of 6.1 min at 3 K. Upon further irradiation at 254 nm, the reverse conversion of •PNH-CO to •NPH-CO along with dehydrogenation to yield PN was observed. The characterization •NPH-CO and •PNH-CO with matrix-isolation IR spectroscopy is supported by D, 15N, and 13C isotope labeling and quantum chemical calculations at the XYGJ-OS/AVTZ level of theory, and the mechanism by hydrogen atom tunneling is consistent with multidimensional instanton theory calculations.