Gas-Phase Oxidation and Nitration of First-, Second-, and Third-Row Atomic Cations in Reactions with Nitrous Oxide: Periodicities in Reactivity

Abstract

Room-temperature reactions of 46 different atomic cations with N2O have been surveyed systematically using an inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. The atomic cations are produced at about 5500 K in the ICP source and are allowed to decay radiatively and thermalize by collisions with Ar and He atoms prior to reaction. Rate coefficients were measured for the reactions of first-row atomic cations from K+ to Se+, of second-row atomic cations from Rb+ to Te+ (excluding Tc+), and of third-row atomic cations from Cs+ to Bi+. Primary reaction channels were observed corresponding to O-atom transfer, N-atom transfer, and N2O addition. Periodicities were observed in overall reaction efficiency, and these are scrutinized in terms of overall exothermicity, the presence of an activation barrier in the reaction coordinate, and the overall conservation of spin. N-atom transfer was observed to compete with O-atom transfer in the reactions of N2O with La+ (4%), Ti+ (22%), Zr+ (45%), Nb+ (35%), Ta+ (40%), and Os+ (60%). Up to three N2O molecules were observed to add sequentially to selected atomic cations as well as several monoxide and dioxide cations. A second O-atom transfer was observed with the group 4, 5, and 6 transition-metal ions (except Mo+) as well as the third-row cations Re+, Os+, Ir+, and Pt+. The atomic ions W+, Os+, and Ir+ formed trioxides in sequential O-atom transfer reactions, and Os+ even formed the tetroxide OsO4+. Multicollision-induced dissociation studies with Ar buffer gas indicated thermodynamically controlled dissociation of TiO2+, ZrO2+, HfO2+, VO2+, NbO2+, TaO2+, and WO2+ by the consecutive detachment of O-atoms while CrO2+, ReO2+, and PtO2+ decomposed primarily by loss of O2 molecules.