Alternative Mechanisms for Solvation Dynamics of Laser-Induced Electrons in Methanol

Abstract

A multiphoton ionization study of neat methanol with subpicosecond 2-eV laser pulses has been previously reported. A hybrid electron solvation mechanism combining both a stepwise transition between two electronsolvent configuration states and a continuous first-order blue shift of the electron absorption spectra was found to closely fit the experimental data. If substantial absorption from free electrons is assumed in this spectral region, we find that another model comprising thermalization prior to a stepwise branching localization without blue-shifting spectra fits equally well at all wavelengths. However, these two models display considerable differences between their respective kinetic parameters, especially the electron localization time. Furthermore, for the nonshifting model, this calculated localization time is considerably longer than that for electron hydration in neat water. We suggest independent studies such as ultrafast electron scavenging experiments before adopting a particular mechanism for electron solvation in methanol.

Electron solvation in methanol revisited

“…Details of the solution procedure and the actual concentration versus time functions can be found at the web-site http://femto.chem.elte.hu/MeOHsolvation/. To ®t the obtained concentration function, the same reconvolution procedure was used as in Turi et al (1997). We have found that mechanism (2) ®ts perfectly the experimental data at all 13 wavelengths analysed between 400 and 1350 nm, which supports the applicability of the model.…”

“…However, there is a great dierence between the two species; while the energetic e À n is directly trapped into a``®nal'' solvated state, the less energetic e À free is trapped in a transient e À tr state, which relaxes to give the same ®nal e À s . We would like to note that mechanism (2) is closely related to the one proposed by Turi et al (1997), with the dierence that the branching is from e À n here, and from e À free there. Supposing that all the elementary steps can be considered as unimolecular reactions and described by ®rst-order kineticsÐwhich is reasonable as the whole solvation is complete within 100 ps that would not allow bimolecular reactions to occurÐwe can solve the according system of dierential equations.…”

“…These laser studies enriched the mechanistic ideas and enabled quantitative testing of kinetic models. A detailed overview of dierent kinetic models can be found in a recent paper of Turi et al (1997). Turi et.…”

“…(1994) comprise kinetic traces in an exceptionally wide wavelength range, from 400 to 1350 nm, obtained following multiphoton ionization of pure methanol at 294 K, with 625 nm (2 eV) laser pulses of approximately 300 fs fwhm, with an irradiance of H10 13 W/cm 2 inside the sample cell. Further details can be found in previous papers (Pe pin et al, 1994;Turi et al, 1997).…”

Building a molecular-level picture of the ultrafast dynamics of the charge-transfer-to-solvent (CTTS) reaction of sodide (Na¯)

“…2, 4, and 7 represent a fit of the solvent-dependent data to what we refer to as "the delayed ejection plus solvation (DE+S) model", as introduced below. The details, assumptions, fitting procedure, and main results have been presented somewhere else [10,25] For the short-time dynamics (t < 10 ps) described by eqs. 1-6, the relevant kinetic parameters are τ 1 (the CTTS electron detachment time), τ 2 (the time for recombination of immediate contact pairs), and p (the fraction of electrons ejected into immediate contact pairs).…”