Adiabatic ionization energies of the overlapped A²A₁and B²E electronic states in CH₃Cl⁺/CH₃F⁺measured with double imaging electron/ion coincidence

Abstract

Utilizing the vacuum ultraviolet (VUV) synchrotron radiation and a double imaging photoelectron photoion coincidence (i(2)PEPICO) technique, we have measured the adiabatic ionization energies (AIEs) of the overlapped A(2)A1 and B(2)E electronic states of CH3Cl(+) and CH3F(+) ions. We show that the two overlapped electronic states can be separated in the electron and ion kinetic energy correlation diagrams based on their state-specific dissociation dynamics, leading to different kinetic energies released in dissociation, along the CH3(+) fragmentation channel. Thus the correlation diagrams yielded values of 13.67 ± 0.03 and 14.77 ± 0.03 eV for the AIEs of the A(2)A1 and B(2)E states of CH3Cl(+), and 16.08 ± 0.03 and 17.00 ± 0.05 eV for CH3F(+), respectively. This method can be generalized to separate ionic states that are otherwise overlapped in normal photoelectron spectra (PES), especially by combining VUV sources and electron/ion coincidence techniques.

Vacuum ultraviolet photodynamics of the methyl peroxy radical studied by double imaging photoelectron photoion coincidences

“…A flow tube combined with a microwave discharge generator was employed as reactor to produce radicals and initiate their reactions. The configurations of the beamline, the i 2 PEPICO spectrometer and the flow tube have already been introduced before [16][17][18][19][20][21] and only a brief description is given here.…”

“…[14][15][16] Particularly, mass-selected threshold PES (ms-TPES) can be measured, which provides high-resolution thermochemical information with structure specific insights. 9,17,18 In this work, we present a detailed VUV photoionization and dissociative photoionization study of CH 3 O 2 by using the high energy resolution of the VUV beamline DESIRS at synchrotron SOLEIL and the state-of-the-art method of double imaging photoelectron photoion coincidence (i 2 PEPICO). 16,19 The full slow photoelectron spectrum (SPES) of CH 3 O 2 is acquired in the 9.7-12.0 eV energy range and assigned with the help of theoretical calculations, which are indispensable as the unfavorable Franck-Condon factors (FCF) combined with the proximity of the first electronically excited state render the measurement of the AIE difficult.…”

Advances in threshold photoelectron spectroscopy (TPES) and threshold photoelectron photoion coincidence (TPEPICO)

“…The measurement of fragment ion velocities from ion images for polyatomic ions was reported by Tang et al, 120 in which the fragment ion translational energies have been used to provide new information about the CH 3 Cl and CH 3 F photoelectron spectra. The results are most dramatic for CH 3 Cl in which the excited A 2 A 1 and B 2 E ion states are overlapped, so that the adiabatic onset for the B state is not resolved.…”

Pyrolysis of n-butane investigated using synchrotron threshold photoelectron photoion coincidence spectroscopy

“…This problem can be overcome by employing position sensitive detectors (PSDs) to collect electrons and ions in coincidences and then the pure TPES of the propyl radical could be acquired with an ion-kinetic-energy-ltered method. 42,43…”