Watching Na atoms solvate into (Na +,e -) contact pairs: Untangling the ultrafast charge-transfer-to-solvent dynamics of Na- in tetrahydrofuran (THF)

Journal of Physical Chemistry A

Volumn 111, Issue 24, 2007, Pages 5144-5157

  Cavanagh, Molly C ^a   Larsen, Ross E ^a   Schwartz, Benjamin J ^a  

^a UNIVERSITY OF CALIFORNIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CONTACT PAIRS; INTRAMOLECULAR RELAXATION; SOLVATION DYNAMICS; SPECTROSCOPIC DYNAMICS;

CHEMICAL RELAXATION; DEGREES OF FREEDOM (MECHANICS); MOLECULAR DYNAMICS; SODIUM COMPOUNDS; SOLVATION; SPECTROSCOPIC ANALYSIS;

DYES;

EID: 34547319413     PISSN: 10895639     EISSN: None     Source Type: Journal    
DOI: 10.1021/jp071132i     Document Type: Article

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55. The zero of time was also allowed to vary in the fitting for each probe wavelength.
56. We note that ref 24 does not present any cross-section data for the solvated electron that is blue of 557 nm, so for wavelengths bluer than this, we assumed that the electron absorption is flat. As discussed in detail in the Supporting Information, this should be a good approximation and it has a negligible effect on our final results.
57. As will be discussed further in the conclusions as well as in ref 26, there is a possibility that the excited CTTS electron could also absorb to some extent in this region.
58. We note that in this spectral region there is no distinction between the DE model presented in ref 25 and the DE+S model presented in ref 26. See the Appendix for details.
59. Although we are unable to test this assumption because there is no wavelength where we can cleanly probe the bleach, we feel that this assumption is reasonable because the sodide CTTS band is expected to have a very similar electronic structure to the hydrated electron, where there is no dynamic solvation seen in the bleach. See refs 43-45
60. We would expect to see spectral diffusion if the experiments were not done with the pump and probe pulses set to magic angle because we know that there is a probe wavelength dependence to the anisotropy in the bleach (see refs 26, 36, and 37).
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63. Because our data was collected at discrete energies, we numerically integrated to obtain the average frequency using the midpoint rule.
64. -) species fits well to a Lorentzian and because we have collected only the high-energy part of the spectrum during this solvation process.
65. -) spectrum to grow in at this wavelength.
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67. - at 400 nm because they assumed that the spectrum had reached equilibrium by ∼4 ps; see the Supporting Information for more details.
68. This solvation process is likely not due to cooling of the sodium atom because it is well-known that the CTTS bands of solutes shift to the blue upon cooling (ref 40), whereas the spectrum of the Na atom that we observe undergoes a dynamic red-shift.
69. As documented in ref 4, the long-time solvation component seen for coumarin 153 in liquid THF is ∼1 ps.
70. Bragg, A. E.; Schwartz, B. J. To be submitted for publication.
71. When we employed this model in our original paper (ref 25), we assumed that the solvent-separated and free electrons did not decay because the decay of both of these species is at least an order of magnitude longer than the ∼10-ps dynamics that we were fitting to the model. In the version of the model employed in this paper, we assumed that the solvent-separated and free electrons recombined on the same (hundreds of ps) time scale, accounting for the small amount of longer-time recombination on the ∼40-ps time scale being considered.
72. Although the experiments done by the Ruhman group have a faster time resolution than the experiments done in our group (∼60 fs vs ∼120 fs), no dynamics have been observed in this system that are faster than the ∼200 fs decay seen at ∼1200 nm. Therefore, even with our slower time resolution, we are able to observe all of the dynamics associated with the sodide CTTS process.