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Title: Effects of molecular rotation after ionization and prior to fragmentation on observed recoil-frame photoelectron angular distributions in the dissociative photoionization of nonlinear molecules

Experimental angle-resolved photoelectron-photoion coincidence experiments measure photoelectron angular distributions (PADs) in dissociative photoionization (DPI) in the reference frame provided by the momenta of the emitted heavy fragments. By extension of the nomenclature used with DPI of diatomic molecules, we refer to such a PAD as a recoil-frame PAD (RFPAD). When the dissociation is fast compared to molecular rotational and bending motions, the emission directions of the heavy fragments can be used to determine the orientation of the bonds that are broken in the DPI at the time of the ionization, which is known as the axial-recoil approximation (ARA). When the ARA is valid, the RFPADs correspond to molecular-frame photoelectron angular distributions (MFPADs) when the momenta of a sufficient number of the heavy fragments are determined. When only two fragments are formed, the experiment cannot measure the orientation of the fragments about the recoil axes so that the resulting measured PAD is an azimuthally averaged RFPAD (AA-RFPAD). In this paper we consider how the breakdown of the ARA due to rotation will modify the observed RFPADs for DPI processes in nonlinear molecules for ionization by light of arbitrary polarization. This model is applied to the core C $1s$ DPI of $${\mathrm{CH}}_{4}$$, with the results compared to experimental measurements and previous theoretical calculations done within the ARA. The published results indicate that there is a breakdown in the ARA for two-fragment events where the heavy-fragment kinetic energy release was less than 9 eV. Finally, including the breakdown of the ARA due to rotation in our calculations gives very good agreement with the experimental AA-RFPAD, leading to an estimate of upper bounds on the predissociative lifetimes as a function of the kinetic energy release of the intermediate ion states formed in the DPI process.
Authors:
 [1] ;  [1]
  1. Texas A & M Univ., College Station, TX (United States). Dept. of Chemistry
Publication Date:
Grant/Contract Number:
SC0012198; A-1020
Type:
Accepted Manuscript
Journal Name:
Physical Review A
Additional Journal Information:
Journal Volume: 93; Journal Issue: 3; Journal ID: ISSN 2469-9926
Publisher:
American Physical Society (APS)
Research Org:
Texas A & M Univ., College Station, TX (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); Robert A. Welch Foundation (United States)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; photodissociation; single- and few-photon ionization & excitation; molecules
OSTI Identifier:
1461974
Alternate Identifier(s):
OSTI ID: 1244783