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

Abstract

We have studied the dissociative recombination of the first three vibrational levels of O 2 ϩ in its electronic ground X 2 ⌸ 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 resolved͒ rate coefficients and the branching fractions near 0 eV collision energy for the vibrational levels vϭ0, 1, and 2. The vibrational populations used were produced in a modified electron impact ion source, which has been calibrated using Cs-O 2 ϩ 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 vϭ0 and goes down by a factor of two or more for vϭ1 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.

Experimental studies of the dissociative recombination of CD3CDOD+and CH3CH2OH$_{2}^+$Unknown node mtable found in MathML fragment.

“…It is reasonable to assume T rot ≈ T vib = 300 K. Equation (4) be used to calculate the thermal rate constant for electron temperatures much higher than 300 K but one should note that the equation does not regard excitation of vibrational and rotational states of higher temperatures. However investigations of the dependence of DR rates on vibrational excitation in the case of O + 2 by Petrignani et al (2005) showed a change of much less than an order of magnitude.…”

Photochemical processes in doped argon-neon core-shell clusters: The effect of cage size on the dissociation of molecular oxygen

“…33, and references therein͒. Here, the matrix cage comes into play because the photoelectron clearly has an increased chance to recombine with O 2 + due to backscattering in the matrix.…”

“…The 1 ⌺ u + potential curve crosses with vibrational states of the molecular ion ͑ =1,2͒ at 12.4 eV and leads to the O͑ 1 S͒ and O͑ 1 D͒ states. 33 Dissociation along this pathway produces photofragments with a kinetic energy of Ϸ0.4 eV.…”

Production of a rovibrationally selected O2+beam for dissociative recombination studies

“…5) can be associated either to IDCE (a, b, c, e) or DDCE (d, f) [3,4,6]. Those processes are indicated below:…”

“…Petrignani et al [3] have developed and characterized an electron impact source, which was installed at the CRYRING storage ring to study the vibrational dependence of the DR rate coefficient through a decomposition of the projected distance spectra recorded under different source conditions. In this paper an alternative method for the production of a rovibrationally selected beam of O + 2 is discussed, which relies on resonance enhanced multiphoton ionization (REMPI) of a gas jet in a dedicated laser ion source.…”