Low-Energy Protons in Strong-Field Dissociation of H ₂ ⁺ via Dipole-Transitions at Large Bond Lengths

Abstract

More than ten years ago, the observation of the low-energy structure in the photoelectron energy spectrum, regarded as an “ionization surprise,” has overthrown our understanding of strong-field physics. However, the similar low-energy nuclear fragment generation from dissociating molecules upon the photon energy absorption, one of the well-observed phenomena in light-molecule interaction, still lacks an unambiguous mechanism and remains mysterious. Here, we introduce a time-energy-resolved manner using a multicycle near-infrared femtosecond laser pulse to identify the physical origin of the light-induced ultrafast dynamics of molecules. By simultaneously measuring the bond-stretching times and photon numbers involved in the dissociation of H2+ driven by a polarization-skewed laser pulse, we reveal that the low-energy protons (below 0.7 eV) are produced via dipole-transitions at large bond lengths. The observed low-energy protons originate from strong-field dissociation of high vibrational states rather than the low ones of H2+ cation, which is distinct from the well-accepted bond-softening picture. Further numerical simulation of the time-dependent Schrödinger equation unveils that the electronic states are periodically distorted by the strong laser field, and the energy gap between the field-dressed transient electronic states may favor the one- or three-photon transitions at the internuclear distance larger than 5 a.u. The time-dependent scenario and our time-energy-resolved approach presented here can be extended to other molecules to understand the complex ultrafast dynamics.

Stereodynamical Control of D3+ Formation from the Bimolecular Photoreaction in the D2–D2 Dimer

“…From a simplified perspective, we directly adopt the potential curves of D 2 + by assuming that the photodissociation of D 2 + in the dimer shares the same mechanism as that in the isolated monomer. As illustrated in Figure b, the dissociation of D 2 + by an intense laser pulse proceeds dominantly via the one-photon and net-two-photon pathways governed by the photon-coupled parallel transition between the 1sσ g and 2pσ u states. , As a result, the dissociation of D 2 + occurs most effectively when the molecule aligns along the polarization direction of the probe pulse, which is confirmed by the alignment effect on the yield of the (D + , D) channel (blue curve in Figure a). For the D 2 –D 2 dimer, neutral fragment D flies along the molecular axis of its dissociating parent D 2 + toward the bound D 2 + , resulting in the formation of D 3 + with a certain probability (see the sketch of the reaction dynamics in Figure a).…”

Twisting attosecond pulse trains by amplitude-polarization IR pulses

“…[37], to control the angular momentum orientation of N 2 molecules. Later on, other molecular scenarios were studied [38][39][40][41][42][43]. This polarization deserves a different classification from linear, circular or elliptical and, taking into account its mathematical expression, we will call it amplitude polarization (AP).…”

Sensitive carbon monoxide detection based on laser absorption spectroscopy with hollow‐core antiresonant fiber

“…[13][14][15][16][17][18][19] Laser absorption spectroscopy based methods are extensively used for trace gas detection. [20][21][22][23][24][25] It has the merits of high sensitivity and high selectivity. [26][27][28][29][30][31][32][33] Among them, tunable diode laser absorption spectroscopy (TDLAS) technology is extensively used in various types of gas detection and offers many advantages such as high sensitivity, low cost, quick response time and noncontact measurement.…”

“…Optical measurement is advanced technique 13–19 . Laser absorption spectroscopy based methods are extensively used for trace gas detection 20–25 . It has the merits of high sensitivity and high selectivity 26–33 .…”