Intramolecular nuclear dynamics in intermolecular Coulombic electron capture

Abstract

We present an analytical model for intermolecular Coulombic electron capture (ICEC) which includes the internal nuclear dynamics of the molecules involved. In ICEC, an electron attaches to an atom or molecule by transferring excess energy to a neighbor, ionizing said neighbor. While previous theoretical investigations assumed fixed nuclei, recent studies indicate that relative motion between the two ICEC partners significantly influences the process. Here, we incorporate the internal nuclear motion of the molecules involved into an analytical equation of the ICEC cross section. We employ two approaches: 1. utilizing theoretical vibrationally resolved photoionization cross sections and 2. applying the Franck-Condon principle. Our theory yields electron spectra, ICEC cross sections for individual vibronic transitions, and temperature dependent cross sections. Nuclear dynamics lead to a distribution of the electronic cross section over several vibrational states and, in our model system H+ LiH, triggers dissociation of LiH during ICEC.

Figures (8)

• Figure 1: Schematic picture of interparticle Coulombic electron capture: A free electron attaches to an atom or molecule by transferring excess energy to a neighbor. If one unit is a molecule, their electron attachment or detachment process, respectively, is coupled to nuclear degrees of freedom. Figure taken from Ref. figshare_figures.
• Figure 2: Energetic representation of ICEC with intramolecular nuclear dynamics: Molecule A binds a free electron of momentum $k$ and transitions from vibronic state $\phi_\mathrm{A}\nu_\mathrm{A}$ to $\phi_{\mathrm{A}^-}\nu_{\mathrm{A}^-}$. Excess energy $\omega$ is transferred to molecule D, ionizing D from $\phi_\mathrm{D}\nu_\mathrm{D}$ to $\phi_{\mathrm{D}^+}\nu_{\mathrm{D}^+}$ with a continuum electron of momentum $k'$. Figure taken from Ref. figshare_figures.
• Figure 3: Potential energy surfaces (black) of the electronic ground states of LiH and LiH$^+$, including the lowest vibrational states and a dissociative state (blue). The dissociation energy $D_\mathrm{e}$, adiabatic and vertical ionization energies $\mathrm{IP}^\mathrm{a}$ and $\mathrm{IP}^\mathrm{v}$, bound and dissociative vibrational energies $E_\nu$ and $E$, respectively, are included for the readers' convenience. $V^\infty_+ - V^\infty$ is the difference between the surfaces at $R\to\infty$. Figure taken from figshare_figures.
• Figure 4: ICEC cross section for H+-LiH vs. incoming electron energy $\varepsilon$ for $R_{\mathrm{H}\mathrm{-LiH}}=3.95\angstrom$. Black: electronic results with vertical ionization of LiH at $R_\mathrm{e}$; red (b-b): with vibrationally resolved cross sections of LiH; blue (b-b FC): based on Franck-Condon model. Only bound-bound transitions of LiH are included. The photorecombination cross section of H+ (dotted gray) is included for comparison. Figures taken from Ref. figshare_figures.
• Figure 5: ICEC cross section for H+-LiH vs. incoming electron energy $\varepsilon$. Black (elec.): electronic results from Fig. \ref{['fig:tot_xs']}. Blue: includes nuclear dynamics of LiH within the Condon approximation; solid (b-b): bound-bound transitions of LiH from Fig. \ref{['fig:tot_xs']}, dashed (b-d): bound-dissociative transitions, dotted (tot): all transitions, coincides with electronic case. Figure taken from Ref. figshare_figures.