Communication: Imaging wavefunctions in dissociative photoionization

Abstract

The dissociative ionization dynamics of excited electronic states of the xenon dimer, Xe2, have been studied using velocity map ion imaging (VMI). A one-colour, (2+1) resonant excitation scheme was employed to first excite and then ionize selected vibrational levels of the Xe2 6p 2[1/2]0 $0_g^ +$0g+ Rydberg state. Cationic fragments were then detected by the VMI. The data provide an outstanding example of the reflection principle in photodissociation with the full nodal structure of the Rydberg state wavefunctions clearly observed in the final Xe+ kinetic energy distributions without the need for scanning the excitation energy. Fitting of the observed distributions provides detailed and precise information on the form of the Xe2+ I(1/2g) potential energy curve involved which is in excellent agreement with the results of photoelectron imaging studies [Shubert and Pratt, J. Chem. Phys. 134, 044315 (2011) 10.1063/1.3533361]. Furthermore, the anisotropy of the product angular distributions yields information on the evolution of the electronic character of the ionic state with internuclear separation, R. The combination of the nature of dissociative ionization and the extent of the bound state wavefunctions provide information over an unusually wide range of internuclear separation R (ΔR > 0.75 Å). This would normally require scanning over a considerable energy region but is obtained in these studies at a fixed excitation energy.

Theoretical study on low-lying electronic states of Kr2+, Xe2+, and Rn2+

“…To achieve reliable theoretical description for these states of Rg 2 + , spin-orbit coupling is essential especially for Kr 2 + and Xe 2 + . For these two ions, the I(3/2u) state originating from 2 u is lower in energy than the I(1/2g) state with origin from 2 g , while the I(1/2g) state lies below the I(3/2u) state in Ne 2 + and Ar 2 + . 10 Furthermore, the I(1/2g) states of Ne 2 + and Ar 2 + possess a double well potential curve, while the I(1/2g) states of Kr 2 + and Xe 2 + have only one minimum due to much more pronounced SOC effects.…”

“…It should be noted that IPs instead of total energies of these states are used to calculate the parameters in Eq. (2). Total energies of these states are equal to the sum of the IPs and energy of the Rg 2 molecule.…”

“…Based on the EOMIP-CCSD approach, energies of all the involved states, i.e., 2 u + , 2 g , 2 u , and 2 g + without SOC and I(1/2u), I(3/2g), I(1/2g), I(3/2u), II(1/2u), II(1/2g) states when SOC is present can be calculated. We proposed the following SOC coupling matrix between 2 + and 2 states:…”

“…By removing one electron from the ground state Rg 2 with an electronic configuration of (σ g ) 2 (π u ) 4 (π g ) 4 (σ u ) 2 , the following low-lying states of Rg 2 + can be reached: 2 u + , 2 g , 2 u , and 2 g + . When spin-orbit coupling (SOC) is present, these states will split to I(1/2u), I(3/2g), I(1/2g), I(3/2u), II(1/2u), II(1/2g), where I and II are used for states of the same symmetry with lower and higher energy, respectively.…”

“…Spectroscopic constants and potential energy curves of low-lying states of rare gas dimer ions (Rg 2 + ) are of great importance in understanding photoionization processes in rare gas dimers, [1][2][3] structures and photodissociation dynamics of rare gas cluster ions, [4][5][6][7] as well as other dynamical processes in chemical physics. By removing one electron from the ground state Rg 2 with an electronic configuration of (σ g ) 2 (π u ) 4 (π g ) 4 (σ u ) 2 , the following low-lying states of Rg 2 + can be reached: 2 u + , 2 g , 2 u , and 2 g + .…”