Intense-Field Multiple-Detachment of F₂¯: Competition with Photodissociation

Abstract

The competition of intense-field multiple-detachment with efficient photodissociation of F¯ is studied as a function of laser peak intensity. The main product channels are disentangled and characterized by 3D coincidence fragment imaging. The presented kinetic energy release spectra, angular distributions, as well as two-color pump-probe measurements allow identification of competing sequential and nonsequential mechanisms. Dissociative detachment, producing two neutral atoms (F + F), is found to be dominated by a sequential mechanism of photodissociation (F¯ + F), followed by detachment of the atomic anion fragment. In contrast, dissociative ionization (F + F) shows competing contributions of both a sequential two-step mechanism as well as a nonsequential double-detachment of the molecular anion, which are distinguished by the kinetic energy released in the dissociation. Triple-detachment is found to be nonsequential in nature and results in Coulomb explosion (F + F). Furthermore, the measured kinetic energy release for dissociation on the Σ state provides a direct measurement of the F¯ dissociation energy, D = 1.26 ± 0.03 eV.

Simultaneous 3D coincidence imaging of cationic, anionic, and neutral photo-fragments

“…We successfully observed four competing channels and their KER. 33 In Fig. 10(a), the observed KER peak for channel F + F is centered at ∼0.4 eV which is assigned to a combination of linear and nonlinear processes.…”

“…10(a), the observed KER peak for channel F + F is centered at ∼0.4 eV which is assigned to a combination of linear and nonlinear processes. 33 Figure 10(b) shows low KER for the F + F channel similar to the F + F channel, which is assigned to a dissociation of F − 2 anion followed by detachment of an electron from atomic F . 33 Figure 10 by instantaneous removal of two electrons from F , whereas the high KER is assigned to a non-sequential process, i.e., removal of two electrons from F − 2 anion followed by dissociation.…”

“…1. For the simulation of the F − 2 photodissociation experiments, 33 the initial parent anion energy is set to E 0 = 2.3 keV, where the U sp and U as potentials supplied to the spectrometer electrodes are set to +0.6 keV and +0.95 keV, respectively. Under these conditions, the electrostatic lens potential shown in Fig.…”

“…Experimentally, four competing processes have been observed for the dissociation of the and Coulomb explosion (F + + F + ). 33 Coincidence detection of all the fragments that are ejected from a single molecule at a time allows taking advantage of total momentum conservation to correct chromatic aberrations in an iterative procedure. First, the sum of all the coincidence fragment momenta of a specific fragmentation event ∆P cm z = ∆P z is estimated using Eq.…”

“…[25][26][27] Using a fast anion beam target and a similar concept of an electrostatic spectrometer, we are able to investigate different competing dissociation and electron detachment channels in intense field interaction with atomic, molecular, and cluster anions. [28][29][30][31][32][33] The photofragment spectrometer design allows coincidence detection of all the possible dissociation products on the same detector, including the anionic, cationic, and neutral fragments. In the present study, we describe the design, calibration, and optimization of the photofragment spectrometer as well as an analytic model for extracting channel specific KER spectra from 3D coincidence imaging data.…”