Fragmentation of long-lived hydrocarbons after strong field ionization

Abstract

We experimentally and theoretically investigated the deprotonation process on nanosecond to microsecond timescale in ethylene and acetylene molecules, following their double ionization by a strong femtosecond laser field. In our experiments we utilized coincidence detection with the reaction microscope technique, and found that both the lifetime of the long-lived ethylene dication leading to the delayed deprotonation and the relative channel strength of the delayed deprotonation compared to the prompt one have no evident dependence on the laser pulse duration and the laser peak intensity. Quantum chemical simulations suggest that such delayed fragmentation originates from the tunneling of near-dissociation-threshold vibrational states through a dissociation barrier on a dication electronic state along C-H stretching. Such vibrational states can be populated through strong field double ionization induced vibrational excitation on an electronically excited state in the case of ethylene, and through intersystem crossing from electronically excited states to the electronic ground state in the case of acetylene.

Three-dimensional momentum imaging of dissociation in flight of metastable molecules

“…One of the striking signatures of dissociation in flight in the coincidence time-of-flight (CTOF) spectrum is a long, curved stripe that extends from the prompt breakup region and terminates at the intact metastable ion time of flight. This signature has been noted in CTOF spectra from a myriad of studies [35][36][37][38][39][40][41][42][43][44][45][46][47][48].…”

“…To demonstrate our approach, we examine the same dissociation-in-flight channel as Larimian et al [47]. Namely, we look at deprotonation of metastable ethylene dications, C 2 H 4 2  + C 2 H 3 + +H + (as well as the deuterated equivalent), using the cold target recoil ion momentum spectroscopy (COLTRIMS) technique [27,28].…”

“…Subsequent studies have implemented this method of lifetime retrieval for other metastable molecules [39,[41][42][43][44]. Recently, making some simplifying assumptions, Larimian et al [47] calculated t d kinematically and retrieved the lifetime for deprotonation of the metastable ethylene dication. They also retrieved the momentum distribution of the fragments using Abel inversion [49] of the position image and discussed possible decay routes.…”

Selection of a Single Isotope of Multiply Charged Xenon (AXez+, A=128–136, z=1–6) by Using a Bradbury–Nielsen Ion Gate

“…MMCs undergo rapid dissociation, namely, a Coulomb explosion, due to strong Coulomb repulsions between positive charges. Molecular structures within a Coulomb explosion have been investigated by using various methods such as covariance mapping, momentum imaging, photoion–photoion‐coincidence spectroscopy, and simple measurements of kinetic energy releases . In contrast, long‐lived MMCs have not been studied in detail.…”

“…The thermal and photochemical reactions of cation radicals have been well explored . However, little is known about MMCs except dications . Since MMCs are metastable in nature, slow dissociation processes, namely, metastable decays and/or post‐source decays (PSDs), are expected to occur when sufficient internal energy is deposited on a precursor MMC.…”