Benchmark Measurements ofH3+Nonlinear Dynamics in Intense Ultrashort Laser Pulses

Abstract

The H(3)(+) ion is the simplest polyatomic molecule and is destined to play a central role in understanding such molecules in intense ultrashort laser pulses. We present the first measurements of the intense field dissociation and ionization of D(3)(+) using coincidence three-dimensional momentum imaging. Our results show features that are a consequence of this molecule's unique equilateral triangular geometry, providing a fundamentally new system for theoretical development.

Elucidating isotopic effects in intense ultrafast laser-driven D2H+fragmentation

“…Recall that a ratio equal to 1 indicates no isotopic effect. Summarizing the main results of this investigation ( figure 3): we observe a large isotopic effect for the single ionization two-body breakup channels, where the H + +D fragmentation, while the first excited state surface leads to three-body fragmentation [20]. For the ground state PES, shown in figure 4(a), there is a deep potential valley along increasing R with r fixed at ∼2.0 a.u., which draws a propagating wavepacket on the surface towards it, favouring two-body breakup over three-body breakup (see the arrow directions).…”

“…And for increasing pulse duration, ionization is expected to occur at larger internuclear distance [24] after the molecule has stretched in intermediate states, resulting in a decrease in the isotopic effect. While a comparison of the ratios for 7 fs pulses at 10 16 W/cm 2 with 40 fs pulses at 5×10 15 W/cm 2 is tentative at best, the general trend observed in figure 3 of a smaller [20]. A scaled cut of this potential for equilateral breakup of the molecule, shown in figure 4(f), indicates that the potential of the H + +D + +D path is lowered (e.g., by 0.5 eV at r scaled = 6 √ m p a.u.)…”

“…+ fragmentation 2 out, by ourselves [20,21,22,23,24] and Alexander et al [25]. Due to its basic structure, measurements of H + 3 can provide a benchmark for theory -and ultimately help develop the theoretical tools needed to explore larger systems, as exemplified by Lötstedt et al [26,27].…”

“…In essence, kinematically-complete information for the nuclear fragments of molecular breakup were recorded, but not the electrons from ionization channels. The KER distributions for each of the channels obtained by this method using 7 fs pulses are plotted in figure 2 with the exception of the three-body dissociation channels, H + +D+D and D + +D+H, where the dissociation rates are extremely low (as is also the case for D + 3 [20]). The figure panels are arranged to compare the distributions of channels where an isotopic effect might arise, and some plots include a statistical weighting factor -for example, the D + +HD channel is statistically twice as probable as the H + +D 2 channel, hence the counts for the H + +D 2 channel have been scaled by a factor of two for comparison purposes.…”

“…This interpretation neglects any effect of the laser field on the subsequent fragmentation dynamics once the nuclear wavepacket is promoted to the PES of the transient D 2 H 2+ . In general, we do not expect that the laser field will play a significant role in those dynamics, as ionization is expected to occur near the peak of the laser field (due to the high-intensity needed to ionize [20,24]) and subsequent nuclear motion unfolds as the laser intensity becomes progressively weaker and less influential. Nevertheless, it is interesting to consider the possible effects of changing the laser intensity and/or pulse duration on the isotopic effect.…”