Few-Femtosecond C₂H₄⁺ Internal Relaxation Dynamics Accessed by Selective Excitation

Abstract

Dissociation of the ethylene cation is a prototypical multistep pathway in which the exact mechanisms leading to internal energy conversions are not fully known. For example, it is still unclear how the energy is exactly redistributed among the internal modes and which step is rate-determining. Here we use few-femtosecond extreme-ultraviolet pulses of tunable energy to excite a different superposition of the four lowest states of C2H4 + and probe the subsequent fast relaxation with a short infrared pulse. Our results demonstrate that the infrared pulse photoexcites the cationic ground state (GS) to higher excited states, producing a hot GS upon relaxation, which enhances the fragmentation yield. As the photoexcitation probability of the GS strongly depends on the molecular geometry, the probing by the IR pulse provides information about the ultrafast excited-state dynamics and the type of conical intersection (planar or twisted) involved in the first 20 fs of the nonradiative relaxation.

Dissociation and Isomerization Following Ionization of Ethylene: Insights from Nonadiabatic Dynamics Simulations

“…The simulations thus indicate a strong excitation-energy dependence of the H-loss yield, in line with experimental data reported by Lucchini et al 13 They employed an XUV-pump NIR-probe scheme and varied the composition of the initial electronic superposition by selecting single harmonics. Approximate H-loss yields can be extracted from a graph in ref 13 displaying static (XUV-pump only) C 2 H 3 + ion yields.…”

Auger–Meitner and X-ray Absorption Spectra of Ethylene Cation: Insight into Conical Intersection Dynamics

“…It is worth noting that in the dynamics study conducted in ref , the simulations commenced from the equilibrium configuration of the D 0 state, with a dihedral angle of 18°, rather than the one of the S 0 state (which has a 0° initial dihedral angle). In contrast, other subsequent dynamics investigations in refs and , initiated their calculations from the S 0 state. Notably, these studies did not reveal any significant involvement of the twisted D 1 / D 0 CI upon excitation to the D 1 state.…”

“…Distinct superpositions of cations can be achieved based on the conditions governing the formation of the initial wave packet, as demonstrated in a recent study by Lucchini et al In the present investigation, we direct our attention to a specific scenario involving the superposition of the D 0 and D 1 states, which has been exploited in ref .…”

“…The relaxation dynamics of the ethylene cation C 2 H 4 + has gained significant attention due to its ultrafast nature. In particular, the photodynamics of the cation is known to proceed through CIs, but despite it being the simplest possible π radical system, the relaxation mechanism has been discussed for more than a decade. − In one of the most recent studies, Zinchenko et al identified the electronic relaxation from the first excited state of the ethylene cation ( D 1 ) to its ground state ( D 0 ) through a planar CI. The most direct evidence of the electronic relaxation was the observation of a short-lived transient feature assigned to the D 1 state in both the experiment (attosecond transient absorption spectroscopy measurements) and ab initio multiple spawning quantum dynamical simulations.…”

Nonadiabatic Photodissociation and Dehydrogenation Dynamics of n-Butyl Bromide Following p-Rydberg Excitation

“…In particular, attention has focused on techniques to synthesize long polyynes, or finite sp-hybridized carbon chains composed of alternating triple and single bonds, given expectations of extraordinary optical, mechanical, and electronic properties . Laser ablation in liquids is a well-established approach for employing high temperatures and pressures formed within a laser plasma to convert organic molecules into new high-value products, including linear carbon chains. , Numerous reports of photoexcited H 2 elimination reactions exist in the literature for gas phase organic neutral − and ionic − molecules. H 2 production is complicated, as it requires two CH dissociations and formation of a new HH bond.…”