Characterization of the I2− anion ground state using conventional and femtosecond photoelectron spectroscopy

Abstract

Femtosecond photoelectron spectroscopy of the I 2 − anion: Characterization of the à ′ 2 Π g,1/2 excited state The X 2 ⌺ u ϩ state of the I 2 Ϫ anion has been fit to a Morse potential using data from two techniques: conventional and femtosecond photoelectron spectroscopy ͑FPES͒. Conventional photoelectron spectroscopy is used to determine the adiabatic electron affinity of I 2 as well as the well depth and equilibrium nuclear geometry of I 2 Ϫ . In the FPES experiment, the pump pulse induces coherent nuclear motion on the ground state of I 2 Ϫ by resonant impulsive stimulated Raman scattering ͑RISRS͒, and the vibrational frequency of the anion is determined from the resulting oscillatory structure in the time-dependent photoelectron spectra. We find the electron affinity ͑EA͒ of I 2 to be 2.524Ϯ0.005 eV, the well depth (D e ) for I 2 Ϫ to be 1.014Ϯ0.005 eV, the equilibrium internuclear separation (R e ) to be 3.205Ϯ0.005 Å, and the vibrational frequency to be 110Ϯ2 cm Ϫ1 . These values for the I 2 Ϫ potential parameters differ significantly from previous results.

Femtosecond Time-Resolved Photoelectron Spectroscopy

“…A subsequent study, 37 performed at higher resolution and simulated with a more accurate experimentally derived anion ground-state potential, 181 produced an accurate potential for the A′ 2 Π g,1/2 dissociative state. These higher-resolution TRPE spectra are displayed in Figure 2.…”

“…In the first example of this type, the pump pulse used to excite the A′ 2 Π g,1/2 r X 2 Σ u + transition in I 2 -was also shown to create a coherent superposition of the v ) 0 and v ) 1 vibrational levels on the ground X 2 Σ u + state, thereby creating a wave packet whose motion could be detected by oscillations in the TRPE spectrum at selected electron kinetic energies. 181 This ground-state excitation process, resonant impulsive stimulated Raman scattering (RISRS), could then be used to obtain the fundamental vibrational frequency of I 2 -, 110 cm In a more sophisticated ground-state wave packet excitation scheme, femtosecond stimulated emission pumping (FSEP), 183 femtosecond pump and dump pulses create a ground-state wave packet with average vibrational energy E exc ) hν pump -hν dump ( Figure 15c). The pump pulse is resonant with the A′ 2 Π g,1/2 r X 2 Σ u + transition, while the dump pulse, applied 50-150 fs after the pump pulse, drives some of the dissociating excited-state wave packet back to the ground state.…”

Two- and three-body photodissociation of gas phase I3−

“…18 -24 In the gas phase, Do et al 25 used collision-induced dissociation of I 3 Ϫ in a tandem mass spectrometer to determine a dissociation energy of 1.31Ϯ0.06 eV for decay to I Ϫ ϩI 2 (X 1 ⌺ g ϩ ). From this value, the spin-orbit coupling constant of the iodine atom, the dissociation energies of I 2 and I 2 Ϫ , 26,27 and the term energies of the A and B states of I 2 , 28,29 one can construct the energy level diagram for I 3 Ϫ and its possible photofragments, Fig. 1.…”

Photodissociation and charge transfer dynamics of negative ions studied with femtosecond photoelectron spectroscopy

“…2, dashed Phys. 107,7613 (1997)]. At high vibrational energies, the modified potential deviates significantly from the previously determined potential.…”