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1. Hydrogen migration in inner-shell ionized halogenated cyclic hydrocarbons

   https://doi.org/10.1038/s41598-023-28694-x  

   Abid, Abdul Rahman; Bhattacharyya, Surjendu; Venkatachalam, Anbu Selvam; Pathak, Shashank; Chen, Keyu; Lam, Huynh Van Sa; Borne, Kurtis; Mishra, Debadarshini; Bilodeau, René C.; Dumitriu, Ileana; et al (February 2023, Scientific Reports)

   Abstract We have studied the fragmentation of the brominated cyclic hydrocarbons bromocyclo-propane, bromocyclo-butane, and bromocyclo-pentane upon Br(3d) and C(1s) inner-shell ionization using coincidence ion momentum imaging. We observe a substantial yield of CH₃⁺fragments, whose formation requires intramolecular hydrogen (or proton) migration, that increases with molecular size, which contrasts with prior observations of hydrogen migration in linear hydrocarbon molecules. Furthermore, by inspecting the fragment ion momentum correlations of three-body fragmentation channels, we conclude that CH_x⁺fragments (withx = 0, …, 3) with an increasing number of hydrogens are more likely to be produced via sequential fragmentation pathways. Overall trends in the molecular-size-dependence of the experimentally observed kinetic energy releases and fragment kinetic energies are explained with the help of classical Coulomb explosion simulations. 

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2. Mechanisms and dynamics of the NH ⁺ ₂ + H ⁺ and NH ⁺ + H ⁺ + H fragmentation channels upon single-photon double ionization of NH ₃

   https://doi.org/10.1088/1361-6455/abc3aa  

   Larsen, Kirk A; Rescigno, Thomas N; Streeter, Zachary L; Iskandar, Wael; Heck, Saijoscha; Gatton, Averell; Champenois, Elio G; Severt, Travis; Strom, Richard; Jochim, Bethany; et al (November 2020, Journal of Physics B: Atomic, Molecular and Optical Physics)

   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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3. Efficiency of charge transfer in changing the dissociation dynamics of OD+ transients formed after the photo-fragmentation of D2O

   https://doi.org/10.1063/5.0159300  

   Iskandar, W; Rescigno, T N; Orel, A E; Severt, T; Larsen, K A; Streeter, Z L; Jochim, B; Griffin, B; Call, D; Davis, V; et al (September 2023, The Journal of Chemical Physics)

   We present an investigation of the relaxation dynamics of deuterated water molecules after direct photo-double ionization at 61 eV. We focus on the very rare D+ + O+ + D reaction channel in which the sequential fragmentation mechanisms were found to dominate the dynamics. Aided by theory, the state-selective formation and breakup of the transient OD+(a1Δ, b1Σ+) is traced, and the most likely dissociation path—OD+: a1Δ or b1Σ+ → A 3Π → X 3Σ− → B 3Σ−—involving a combination of spin–orbit and non-adiabatic charge transfer transitions is determined. The multi-step transition probability of this complex transition sequence in the intermediate fragment ion is directly evaluated as a function of the energy of the transient OD+ above its lowest dissociation limit from the measured ratio of the D+ + O+ + D and competing D+ + D+ + O sequential fragmentation channels, which are measured simultaneously. Our coupled-channel time-dependent dynamics calculations reproduce the general trends of these multi-state relative transition rates toward the three-body fragmentation channels. 

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4. Controlling H3+ Formation From Ethane Using Shaped Ultrafast Laser Pulses

   https://doi.org/10.3389/fphy.2021.691727  

   Townsend, Tiana; Schwartz, Charles J.; Jochim, Bethany; P., Kanaka Raju; Severt, T.; Iwamoto, Naoki; Napierala, J. L.; Feizollah, Peyman; Tegegn, S. N.; Solomon, A.; et al (June 2021, Frontiers in Physics)

   null (Ed.)

   An adaptive learning algorithm coupled with 3D momentum-based feedback is used to identify intense laser pulse shapes that control H 3 + formation from ethane. Specifically, we controlled the ratio of D 2 H + to D 3 + produced from the D 3 C-CH 3 isotopologue of ethane, which selects between trihydrogen cations formed from atoms on one or both sides of ethane. We are able to modify the D 2 H + : D 3 + ratio by a factor of up to three. In addition, two-dimensional scans of linear chirp and third-order dispersion are conducted for a few fourth-order dispersion values while the D 2 H + and D 3 + production rates are monitored. The optimized pulse is observed to influence the yield, kinetic energy release, and angular distribution of the D 2 H + ions while the D 3 + ion dynamics remain relatively stable. We subsequently conducted COLTRIMS experiments on C 2 D 6 to complement the velocity map imaging data obtained during the control experiments and measured the branching ratio of two-body double ionization. Two-body D 3 + + C 2 D 3 + is the dominant final channel containing D 3 + ions, although the three-body D + D 3 + + C 2 D 2 + final state is also observed. 

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5. Disentangling sequential and concerted fragmentations of molecular polycations with covariant native frame analysis

   https://doi.org/10.1039/d2cp03029b  

   McManus, Joseph W.; Walmsley, Tiffany; Nagaya, Kiyonobu; Harries, James R.; Kumagai, Yoshiaki; Iwayama, Hiroshi; Ashfold, Michael N.R.; Britton, Mathew; Bucksbaum, Philip H.; Downes-Ward, Briony; et al (September 2022, Physical Chemistry Chemical Physics)

   We present results from an experimental ion imaging study into the fragmentation dynamics of 1-iodopropane and 2-iodopropane following interaction with extreme ultraviolet intense femtosecond laser pulses with a photon energy of 95 eV. Using covariance imaging analysis, a range of observed fragmentation pathways of the resulting polycations can be isolated and interrogated in detail at relatively high ion count rates (∼12 ions shot −1 ). By incorporating the recently developed native frames analysis approach into the three-dimensional covariance imaging procedure, contributions from three-body concerted and sequential fragmentation mechanisms can be isolated. The angular distribution of the fragment ions is much more complex than in previously reported studies for triatomic polycations, and differs substantially between the two isomeric species. With support of simple simulations of the dissociation channels of interest, detailed physical insights into the fragmentation dynamics are obtained, including how the initial dissociation step in a sequential mechanism influences rovibrational dynamics in the metastable intermediate ion and how signatures of this nuclear motion manifest in the measured signals. 

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