The vibrational spectra of molecular ions isolated in solid neon. IV. NO+, NO−, ONNO+, and ONNO−

When a Ne:NO sample is codeposited at approximately 5 K with a beam of neon atoms that has been excited in a microwave discharge, photoionization and Penning ionization of the NO lead to the stabilization of both monomer and dimer ions. The most prominent infrared absorption, at 1619.2 cm−1, results from the reaction of NO− with NO or of an electron with (NO)2 to form the charge-delocalized trans-ONNO− species. The position of the totally symmetric NO-stretching absorption of trans ONNO− can be inferred from observation of a combination band. The infrared absorption of NO+ has been detected very close to the gas-phase band center. Other infrared absorptions have been tentatively assigned to NO−, cis ONNO−, trans ONNO, and the lowest energy isomer of ONNO+. Comparison of the gas-phase vibrational frequencies observed for the weakly bound species cis ONNO and N2O3 with the corresponding frequencies observed in this neon-matrix study suggests that the matrix shifts for the dimer ion absorptions in the mid-infrared probably amount to less than 1%.