Photodissociation dynamics of CH₃I probed via multiphoton ionisation photoelectron spectroscopy

Abstract

Femtosecond photoelectron spectroscopy measurements of dissociation CH3I show complex dynamics in the high energy region of absorption band A.

Photodissociation dynamics of methyl iodide probed using femtosecond extreme ultraviolet photoelectron spectroscopy

“…As observed in previous UV photoionisation of the excited state, the crosssection into the upper spin-orbit state of the X state of the CH 3 I + cation is higher than that of the lower spin-orbit state. 22 The broad feature in the excited state spectrum at a binding energy of 8 eV is reminiscent of the feature in the ground state spectrum at 12.5 eV that corresponds to ionisation to the A-state of the ion, having a similar difference in energy to the lowest ion state. Ionisation from the neutral excited state into the A ion state would, however, be a 2 electron transition, meaning this is strongly forbidden.…”

“…Along the dissociative coordinate, the wavepacket passes a crossing between the 3 Q 0 and 1 Q 1 states where population transfer can occur, leading to formation of both the ground I( 2 P 3/2 ) and excited I*( 2 P 1/2 ) spin-orbit states of atomic iodine, in conjunction with the ground state methyl radical. This relatively simple picture of the dynamics has been shown to be consistent along a reasonable range of energies on the red side of the A-band, 10,11,[15][16][17][18][19][20][21][22] although recent photoelectron spectroscopy measurements suggest the dynamics on the blue side may not be so straight forward. 22 To date there have been surprisingly few measurements of the excited state dynamics of the A-band when compared with measurements of the product state distributions.…”

“…This relatively simple picture of the dynamics has been shown to be consistent along a reasonable range of energies on the red side of the A-band, 10,11,[15][16][17][18][19][20][21][22] although recent photoelectron spectroscopy measurements suggest the dynamics on the blue side may not be so straight forward. 22 To date there have been surprisingly few measurements of the excited state dynamics of the A-band when compared with measurements of the product state distributions. The dynamics have been probed using Coulomb explosion imaging, 10,23,24 XUV transient absorption spectroscopy 11,25 and multiphoton ionisation photoelectron spectroscopy.…”

“…11 The multiphoton ionisation photoelectron spectroscopy experiments provide timeframes for exiting the Franck-Condon region but the limited ionisation energy means the reaction cannot be followed to extended bond lengths. 22 Here we report new XUV photoelectron spectroscopy measurements of the photodissociation dynamics of methyl iodide towards the red side of the A-band, following excitation at 269 nm.…”

“…The dynamics have been probed using Coulomb explosion imaging, 10,23,24 XUV transient absorption spectroscopy 11,25 and multiphoton ionisation photoelectron spectroscopy. 22 The CEI experiments show strong sensitivity to geometry changes at extended bond lengths, but struggle to capture the early time (o100 fs) dynamics due to limited temporal resolution and/or strong field effects in the probe process. 10,23,24 The XUV transient absorption experiments, meanwhile, are sensitive to the intermediate transition state region, providing a timeframe for transition through this region, but they do not show structural sensitivity.…”