Abstract The gas-phase reaction of O + H 3 + has two exothermic product channels: OH + + H 2 and H 2 O + + H. In the present study, we analyze experimental data from a merged-beams measurement to derive thermal rate coefficients resolved by product channel for the temperature range from 10 to 1000 K. Published astrochemical models either ignore the second product channel or apply a temperature-independent branching ratio of 70% versus 30% for the formation of OH + + H 2 versus H 2 O + + H, respectively, which originates from a single experimental data point measured at 295 K. Our results are consistent with this data point, but show a branching ratio that varies with temperature reaching 58% versus 42% at 10 K. We provide recommended rate coefficients for the two product channels for two cases, one where the initial fine-structure population of the O( 3 P J ) reactant is in its J = 2 ground state and the other one where it is in thermal equilibrium.
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Mechanisms and dynamics of the NH + 2 + H + and NH + + H + + H fragmentation channels upon single-photon double ionization of NH 3
Abstract We present state-selective measurements on the N H 2 + + H + and NH + + H + + H dissociation channels following single-photon double ionization at 61.5 eV of neutral NH 3 , where the two photoelectrons and two cations are measured in coincidence using 3D momentum imaging. Three dication electronic states are identified to contribute to the N H 2 + + H + dissociation channel, where the excitation in one of the three states undergoes intersystem crossing prior to dissociation, producing a cold N H 2 + fragment. In contrast, the other two states directly dissociate, producing a ro-vibrationally excited N H 2 + fragment with roughly 1 eV of internal energy. The NH + + H + + H channel is fed by direct dissociation from three intermediate dication states, one of which is shared with the N H 2 + + H + channel. We find evidence of autoionization contributing to each of the double ionization channels. The distributions of the relative emission angle between the two photoelectrons, as well as the relative angle between the recoil axis of the molecular breakup and the polarization vector of the ionizing field, are also presented to provide insight on both the photoionization and photodissociation mechanisms for the different dication states.
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- Award ID(s):
- 1807017
- PAR ID:
- 10431495
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Date Published:
- Journal Name:
- Journal of Physics B: Atomic, Molecular and Optical Physics
- Volume:
- 53
- Issue:
- 24
- ISSN:
- 0953-4075
- Page Range / eLocation ID:
- 244003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1088/1361-6455/abc3aa
