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Feizollah, Peyman

Publications and source records attributed to Feizollah, Peyman.

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Native frames: An approach for separating sequential and concerted three-body fragmentation

Disentangling sequential and concerted three-body fragmentation has been a longstanding endeavor in studies of molecular dynamics. To accomplish this goal, we recently introduced a novel method to separate sequential from concerted breakup, where the sequential events are analyzed in their native frames [J. Rajput et al., Phys. Rev. Lett. 120, 103001 (2018)]. The essence of this method is the use of the Jacobi coordinates' conjugate momenta to reduce the dimensionality of the multibody fragmentation in combination with a clear signature for sequential breakup. To demonstrate this method, we employ coincidence momentum imaging to study the strong-field dissociative ionization of OCS into O + +C + + S + , which typically undergoes concerted fragmentation or sequential breakup involving either a metastable CO 2+ or CS 2+ molecule. We identify sequential breakup using a uniform distribution as a function of the angle between the conjugate momenta, associated with the first and second fragmentation steps, which is due to the rotation of the intermediate molecule in the fragmentation plane. Furthermore, by exploiting this uniform distribution, we separate the sequential and concerted distributions in any plot created from the measured momenta.

Atomic & molecular processes in external fields↗
DOE OSTI2021

Controlling $H_{3}^{+}$ Formation From Ethane Using Shaped Ultrafast Laser Pulses

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.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Strong-field-induced bond rearrangement in triatomic molecules

A comparative study of bond rearrangement is reported for the double ionization of three triatomic molecules: carbon dioxide, carbonyl sulfide, and water (D 2 O). Specifically, we study the formation of the molecular cation AC + from the edge atoms of a triatomic molecular dication ABC 2+ following double ionization by intense, short (23 fs, 790 nm) laser pulses. The comparison is made using the double ionization branching ratio of each molecule, thereby minimizing differences due to differing ionization rates. The rearrangement branching ratio is highest for water, which has a bent initial geometry, while CO 2 and OCS are linear molecules. The angular distribution of O 2 + fragments arising from CO 2 is essentially isotropic, while SO + from OCS and $D$ $^{+}_{2}$ from D 2 O are aligned with the laser polarization. In the CO 2 and D 2 O cases, the angular distributions of the bond rearrangement channels are different from the angular distributions of the dominant dissociative double ionization channels CO + + O + and OD + + D + . Only the angular distribution of SO+ from OCS is both aligned with the laser polarization and similar to the angular distribution of the largest dissociative channel, CO + + S + . As a result, the mixed behavior observed from the angular distributions of the different molecules stands in contrast to the relative consistency of the magnitude of the bond rearrangement branching ratio.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Dependence on the Initial Configuration of Strong Field-Driven Isomerization of C 2 H 2 Cations and Anions

In this work, we have investigated the femtosecond laser-induced fragmentation of $C_{2}H_{2}^{q}$ ion beam targets in various initial configurations, including acetylene (linear HCCH), vinylidene (H 2 CC), and cis/trans. The initial configuration is shown to have a tremendous impact on the branching ratio of acetylene-like (CH q1 + CH q2 ) and vinylidene-like ($CH^{q'_{1}}$ + $CH^{q'_{2}}_{2}$) dissociation of a specific $C_{2}H_{2}^{q}$ molecular ion. In particular, whereas $C_{2}H_{2}^{+}$ monocation generated from C 2 H 2 , a linear HCCH target, exhibits comparable levels of acetylene-like and vinylidene-like fragmentation, vinylidene or cis/trans configuration ion beams preferably undergo vinylidene-like fragmentation, with an acetylene branching ratio ranging from 13.9% to zero.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

H2 roaming chemistry and the formation of H3+ from organic molecules in strong laser fields

Roaming mechanisms, involving the brief generation of a neutral atom or molecule that stays in the vicinity before reacting with the remaining atoms of the precursor, are providing valuable insights into previously unexplained chemical reactions. Here in this paper, the mechanistic details and femtosecond time-resolved dynamics of H 3 + formation from a series of alcohols with varying primary carbon chain lengths are obtained through a combination of strong-field laser excitation studies and ab initio molecular dynamics calculations. For small alcohols, four distinct pathways involving hydrogen migration and H 2 roaming prior to H 3 + formation are uncovered. Despite the increased number of hydrogens and possible combinations leading to H 3 + formation, the yield decreases as the carbon chain length increases. The fundamental mechanistic findings presented here explore the formation of H 3 +, the most important ion in interstellar chemistry, through H 2 roaming occurring in ionic species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Mechanisms and time-resolved dynamics for trihydrogen cation (H 3 +) formation from organic molecules in strong laser fields

Strong-field laser-matter interactions often lead to exotic chemical reactions. Trihydrogen cation formation from organic molecules is one such case that requires multiple bonds to break and form. Here, we present evidence for the existence of two different reaction pathways for H 3 + formation from organic molecules irradiated by a strong-field laser. Assignment of the two pathways was accomplished through analysis of femtosecond time-resolved strong-field ionization and photoion-photoion coincidence measurements carried out on methanol isotopomers, ethylene glycol, and acetone. Ab initio molecular dynamics simulations suggest the formation occurs via two steps: the initial formation of a neutral hydrogen molecule, followed by the abstraction of a proton from the remaining CHOH 2+ fragment by the roaming H 2 molecule. This reaction has similarities to the H 2 +H 2 + mechanism leading to formation of H 3 + in the universe. These exotic chemical reaction mechanisms, involving roaming H 2 molecules, are found to occur in the ~100 fs timescale. Roaming molecule reactions may help to explain unlikely chemical processes, involving dissociation and formation of multiple chemical bonds, occurring under strong laser fields.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗