Radiative lifetimes of metastable O+2(a 4Πu) and NO+(a 3Σ+)

Vibrationally resolved rate coefficients and branching fractions in the dissociative recombination of O2+

We have studied the dissociative recombination of the first three vibrational levels of O(2) (+) in its electronic ground X (2)Pi(g) state. Absolute rate coefficients, cross sections, quantum yields and branching fractions have been determined in a merged-beam experiment in the heavy-ion storage ring, CRYRING, employing fragment imaging for the reaction dynamics. We present the absolute total rate coefficients as function of collision energies up to 0.4 eV for five different vibrational populations of the ion beam, as well as the partial (vibrationally resolved) rate coefficients and the branching fractions near 0 eV collision energy for the vibrational levels v=0, 1, and 2. The vibrational populations used were produced in a modified electron impact ion source, which has been calibrated using Cs-O(2)(+) dissociative charge transfer reactions. The measurements indicate that at low collision energies, the total rate coefficient is weakly dependent on the vibrational excitation. The calculated thermal rate coefficient at 300 K decreases upon vibrational excitation. The partial rate coefficients as well as the partial branching fractions are found to be strongly dependent on the vibrational level. The partial rate coefficient is the fastest for v=0 and goes down by a factor of two or more for v=1 and 2. The O((1)S) quantum yield, linked to the green airglow, increases strongly upon increasing vibrational level. The effects of the dissociative recombination reactions and super elastic collisions on the vibrational populations are discussed.

Fourier transform ion cyclotron resonance detection of multiphoton ionization spectroscopy

Fourier transform ion cyclotron resonance (FT-ICR) detection was tested for resonanceenhanced multiphoton ionization (REMPI) spectroscopy. The (2+1) REMPI spectra of acetaldehyde were obtained in the wavelength range 364-354 nm via a two-photon resonant 3s ← n Rydberg transition. The space-charge effects on the REMPI spectra were examined in the vicinity of the 0 0 (0) transition. The trapping efficiency measurement shows that all the ions produced from REMPI dissociation processes are arrested in the ion cyclotron resonance cell even in the presence of space-charge interactions. Axial kinetic energy release distributions of ions were extracted from the trapping efficiency data obtained under a new space-charge-free condition. FT-ICR peak heights were measured as a function of pressure at different laser powers, magnetic field strengths, and ion excitation methods to test for the detection linearity. The FT-ICR detection responds linearly to the number of ions in a low pressure limit. The product branching ratio was measured by using various ion excitation methods and was compared with the previous quadrupole mass spectrometric study. FT-ICR detection yields the mass-selected REMPI spectra and the product branching ratio in the absence of kinetic shifts.