I − ⋅ CH 3 X  (X=Cl,Br,I) photodetachment: The effect of electron-molecule interactions in cluster anion photodetachment spectra and angular distributions

Abstract

The electron kinetic energy dependence of the photoelectron spectra and angular distributions of I(-)⋅CH(3)X (X=Cl,Br,I) cluster anions are measured via velocity mapped imaging at wavelengths between 350 and 270 nm. Processes analogous to those encountered in free CH(3)X-electron interactions are revealed. In particular, the presence and energies of resonances associated with a low lying σ(∗) state have a marked effect on the results of I(-)⋅CH(3)X photoexcitation. These effects (vibrational excitation, product anion production, and alteration of the photoelectron angular distribution) are far more prominent for I(-)⋅CH(3)I. However, in the vicinity of the (2)P(1/2) threshold there is a sharp deviation in the (2)P(3/2) channel angular distribution and an enhancement of the (2)P(3/2) channel vibrational structure of all three cluster anions. These latter effects are specific to the cluster anion environment through the relaxation of the partner excited I atom and subsequent electronic autodetachment.

Inter-channel effects in monosolvated atomic iodide cluster anion detachment: Correlation of the anisotropy parameter with solvent dipole moment

“…Vibrational structure associated with anion induced distortion of the molecular moiety in monosolvated iodide has also been reported in I − · CH 3 Cl, I − · CH 3 Br, and I − · CH 3 I. 4 However, in the majority of reported atomic iodide cluster anions the distortion of the molecular moiety is minor, resulting in very little vibrational structure in the pho- toelectron spectrum. 17,[19][20][21][22] Similarly, spectra extracted from our images of I − · X (X = C 4 H 5 N, (CH 3 ) 2 CO, CH 3 NO 2 ) show very little evidence of vibration.…”

“…The PAD is eKE dependent, but β(eKE) is well characterized for free I − detachment via the 2 P 3/2 channel. 4 Near threshold, β ≈ 0 (an isotropic distribution), becomes more negative (polarization of the distribution perpendicular to ε p ) as the eKE increases until a minimum is reached (≈0.9 eV) and the trend reverses. A portion of this range (0.80-1.05 eV) is shown in Fig.…”

“…Combining photoelectron imaging and a tunable photon source, the effect of a low-lying methyl halide σ * resonance on I − · CH 3 Y (Y = Cl, Br, I) photodetachment has been recently demonstrated. 2,4,9 A particularly striking demonstration of this effect is seen in the comparison of photoelectron images for I − and I − · CH 3 I.…”

“…[1][2][3][4][5][6] Subject to minor perturbation from the molecular moiety, the highest lying occupied orbitals are essentially those of free I − . 2,3,5,[7][8][9][10] The cluster anion detachment spectra are similar to those of free I − and the transitions observed are most conveniently discussed according to the asymptotic atomic iodine states produced.…”

Solvation effects on angular distributions in H−(NH3)n and NH2−(NH3)n photodetachment: Role of solute electronic structure

“…[23][24][25] The third (post-detachment) motif, manifest in the presence of electron-solvent scattering resonances, was also discussed in several recent publications. [23][24][25][26][27] In this work, we address the effect of solvation-induced changes in the parent orbital symmetry (i.e., the second of the above motifs) by examining PADs for two solvation series, with the same solvent but different solutes with distinct parent orbitals.…”