Solvent resonance effect on the anisotropy of NO−(N2O)n cluster anion photodetachment

Abstract

Photodetachment from NO(-)(N(2)O)(n) cluster anions (n< or =7) is investigated using photoelectron imaging at 786, 532, and 355 nm. Compared to unsolvated NO(-), the photoelectron anisotropy with respect to the laser polarization direction diminishes drastically in the presence of the N(2)O solvent, especially in the 355 nm data. In contrast, a less significant anisotropy loss is observed for NO(-)(H(2)O)(n). The effect is attributed to photoelectron scattering on the solvent, which in the N(2)O case is mediated by the (2)Pi anionic resonance. No anionic resonances exist for H(2)O in the applicable photoelectron energy range, in line with the observed difference between the photoelectron images obtained with the two solvents. The momentum-transfer cross section, rather than the total scattering cross section, is argued to be an appropriate physical parameter predicting the solvent effects on the photoelectron angular distributions in these cluster anions.

Further Evidence for Resonant Photoelectron−Solvent Scattering in Nitrous Oxide Cluster Anions

“…We now move on to the solvation effects on the photoelectron angular distributions in the photodetachment of NO -(Ν 2 ) n , n ) 1-7 (type I transitions in Figure 1) and O -(Ν 2 ) n , n ) 4-9. The anisotropy values ( ) for the two cluster series, derived from the present work as well as past measurements, 8,21 are plotted in Figure 2a,b, respectively, as functions of eKE. The following analysis closely follows the procedure outlined previously.…”

“…The resulting curve closely matches the curve first computed by Cooper and Zare. 3 The NO -curve in Figure 2a has been adjusted relative to that used previously 8 The effects of solvent-induced perturbations of the final and initial photoelectron wave functions can now be quantified by calculating the difference between the experimental values for cluster anions and the Cooper-Zare predictions for the unsolvated core anions at the observed transition's peak eKE. When the results for clusters of different sizes are compared, the difference between the experimental values, (eKE), and the Cooper-Zare predictions, cz (eKE), should be normalized by the corresponding degree of solvation.…”

“…8 When plotted as a function of eKE, the resulting anisotropy differentials peaked at approximately the same energy as a computed momentum-transfer cross-section for electron collisions with N 2 O (∼2.25 eV). 15 The same analysis for 355 nm detachment from NO -(H 2 O) n (n ) 1-3, peak eKE ) 0.9-2.13 eV) yielded a less pronounced loss of anisotropy with a different energy dependence, confirming that the effect is specific to the N 2 O solvent.…”

“…The values for the NO --based transitions (band I), including bare NO -, are plotted in Figure 2a as a function of the transition's peak eKE, along with the previous results for this cluster series at 786, 532, and 355 nm, 8 with error bars of (2 standard deviations. The data point for bare NO -at 266 nm in Figure 2a reflects the results of the new measurement only (without combining it with past data), as the present work was carried out with significantly lower experimental backgrounds and greater data accumulation times (as evidenced by the excellent quality of the photoelectron image in Figure 1 …”

Vibronic coupling in the superoxide anion: The vibrational dependence of the photoelectron angular distribution

“…1,28,35 Among other anions, the prominent dependence of photoelectron anisotropy on the final vibrational state of the neutral was reported in the photodetachment of NO − . 39 In the case of neutral diatomic molecules, dramatic changes in the PAD have been observed between different vibronic photoionization bands of N 2 , CO, and O 2 . [40][41][42] Such effects are associated with strong coupling of the electronic and vibrational motion and usually a breakdown of the Born-Oppenheimer approximation as a consequence of excitation of intermediate, autoionizing Rydberg states or shape resonances.…”