New Insights into the Charge-Transfer-to-Solvent Spectrum of Aqueous Iodide: Surface versus Bulk

Abstract

Liquid phase charge-transfer-to-solvent (CTTS) transitions are important, as they serve as photochemical routes to solvated electrons. In this work, broadband deep-ultraviolet electronic sum frequency generation (DUV-ESFG) and two-photon absorption (2PA) spectroscopic techniques were used to assign and compare the nature of the aqueous iodide CTTS excitations at the air/water interface and in bulk solution. In the one-photon absorption (1PA) spectrum, excitation to the 6s Rydberg-like orbital (5p→6s) gives rise to a pair of spin-orbit split iodine states, 2 P3/2 and 2 P1/2. In the 2PA spectra, the lower energy 2 P3/2 peak is absent, and the observed 2PA peak, which is ~0.14 eV blue-shifted relative to the upper 2 P1/2 CTTS peak seen in 1PA, arises from 5p→6p electronic promotion. The band observed in the ESFG spectrum is attributed to mixing of excited states involving 5p→6p and 5p→6s promotions caused by both vibronic coupling and the external electric field generated by asymmetric interfacial solvation.

Natural Charge-Transfer Analysis: Eliminating Spurious Charge-Transfer States in Time-Dependent Density Functional Theory via Diabatization, with Application to Projection-Based Embedding

“…[9][10][11][12][13][14][15][16][17][18][19][20] Due to the intimate participation of the solvent, CTTS states provide a useful experimental handle for investigating local solvation structure. [21][22][23][24] CTTS excitation of solutes such as I − (aq) and CN − (aq) is a standard means to generate hydrated electrons in the laboratory. 25,26 Aside from its exotic nature as a quantum-mechanical solute, [27][28][29][30] e − (aq) is a byproduct of water radiolysis 26,31 and is frequently implicated in DNA damage by ionizing radiation.…”

In Situ Spectroscopic Probing of Polarity and Molecular Configuration at Aerosol Particle Surfaces

“…Increasing evidence shows that naturally occurring organic materials reside preferentially at aerosol particle surfaces. ,− The organic materials at the surfaces can affect atmospheric compositions by changing the heterogeneous chemistry, optical properties, and ice and cloud nucleating abilities of atmospheric aerosols. ,, The surfaces of aerosol particles are expected to exhibit unique physical and chemical properties. As such, the structure, mass transport kinetics, molecular-level dynamics, and heterogeneous chemical reactions in the surface regions of aerosol particles are different than those of their corresponding bulks. ,,, Recently, tremendous efforts have been made on physical properties and chemical reactions at aerosol particle surfaces. − ,− Despite these efforts, only some indirect evidence was provided regarding the surface properties of aerosols. However, their chemical activities and physical properties at aerosol surfaces have not been examined directly because of a lack of suitable tools for in situ surface-specific measurements.…”

Electronic Structure of Liquid Alkanes: A Representative Case of Liquid Hexanes and Cyclohexane Studied Using Polarization-Dependent Two-Photon Absorption Spectroscopy

“…Our approach thus emphasizes the usefulness of the isolated-molecule electronic structure calculation as a reasonable starting point to investigate the fate of electronic transitions in the condensed phase, particularly for molecules with no low-lying valence excitations. 57 V.B. Liquid Hexanes.…”

“…We re-emphasize that except for shifting transitions ending in the 3s Rydberg state, the calculated gas phase transition energies (after correction) and relative oscillator strengths are used unaltered in our simulation of the liquid phase spectra. Our approach thus emphasizes the usefulness of the isolated-molecule electronic structure calculation as a reasonable starting point to investigate the fate of electronic transitions in the condensed phase, particularly for molecules with no low-lying valence excitations …”