One-color multiphoton threshold photoelectron spectra of methyl bromide, and their comparison with methyl iodide

Abstract

Threshold photoelectron spectra (ZEKE) of methyl iodide, bromide, and chloride are investigated using a one-color, two-photon ionization. Resonances due to a dissociative intermediate state are responsible for differences between spectra of the three halides, with long progressions in the C–I stretching vibration being observed in CH3I, where the one photon absorption is near the maximum of the dissociative continuum, while the vibrational structure is much less prominent in the lighter halides, where this does not occur. The spectra provide accurate ionization potentials of the three compounds as well as insights into their dissociation dynamics, and extensive information about the vibrational structure of their cations.

UV photodissociation of methyl bromide and methyl bromide cation studied by velocity map imaging

“…Two-photon threshold photoelectron spectra shows that photoionization onto X 2 E 3/2 dominates. 40 If A 2 A 1 was the dissociating state accessed directly by CH 3 Br + absorption of a 330 nm photon, the angular distribution would be expected to be perpendicular, yet we observe a parallel process. Thus an indirect dissociation process must be important.…”

Time-resolved high-harmonic spectroscopy of the photodissociation of CH3I and CF3I

“…The cationic states were constructed using a Morse potential for a pseudodiatomic molecule. The X + states were modeled with the equilibrium distance Req = 2.126Å [41], the ground state vibrational wavenumberν 0 = 478.0 cm −1 [42], the dissociation energy De = 2.731 eV [43], the adiabatic ionisation energy Ip = 9.538 eV [44] to the X + 2 E 3/2 state and the spin-orbit splitting of 5050 cm −1 [45]. The parametersν 0 = 296.3 cm −1 , De = 0.925 eV, the zero point energy Te = 11.944 eV (all from [45]) and Req = 2.503Å [41] were used for the A + state.…”

Photoelectron spectroscopic study of the E⊗e Jahn–Teller effect in the presence of a tunable spin–orbit interaction. I. Photoionization dynamics of methyl iodide and rotational fine structure of CH3I+ and CD3I+

“…Theoretical studies of the Jahn-Teller effect have been reported that account for the vibronic structure observed in these He I photoelectron spectra. [12][13][14] Mass-analyzed thresholdionization (MATI) and pulsed-field-ionization zero-kineticenergy (PFI-ZEKE) photoelectron spectra of theX + ←X transitions of CH 3 I, its fully deuterated isotopomer CD 3 I, and CH 3 Br with partial resolution of the rotational structure have also been recorded and analyzed, [15][16][17][18][19][20] providing insights into the complex interplay of vibronic, spin-orbit, and rotational effects in Jahn-Teller-coupled systems.…”