Ultraviolet charge-transfer-to-solvent spectroscopy of halide and hydroxide ions in subcritical and supercritical water

Abstract

Exploring charge-transfer-to-solvent excitation of aqueous halide anions by vacuum ultraviolet spectroscopy – new insights up to 380 °C.

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

“…Based on the excited state energies of xenon, we expect the lowest energy two-photon allowed transition ( 1 S0→5p 5 ( 2 P3/2)6p) to be centered ~0.12-0.25 eV above the upper CTTS transition in 1PA originating from the 1 S0→ 5p 5 ( 2 P1/2)6s excitation. This is consistent with our measured 2PA spectra, which peaks ~0.14 eV higher in energy, as compared to the upper component of the 1PA spectra, 9 shown in Fig. 2(c).…”

“…The latter increasingly interferes with the shorter wavelength region of the 1PA spectra. 9 Herein, we present aqueous iodide CTTS spectra measured with interface-sensitive femtosecond broadband deep-ultraviolet electronic sum frequency generation (DUV-ESFG) spectroscopy and bulk-sensitive two-photon absorption (2PA) spectroscopy, and discuss the salient selection rules and symmetry arguments within a Rydberg transition model to provide insight into the aqueous iodide CTTS spectrum, specifically in the region of overlapping transitions. Moreover, the interference from water electronic absorption is avoided by virtue of using non-linear processes to access the halide electronic absorption.…”

“…CTTS states are short-lived excited states that comprise a neutral parent atom and an excited electron in a dipole-bound state supported by the surrounding solvent network. Because the initial and final states are defined by the parent ion and the surrounding solvent, CTTS spectra are highly sensitive to the environment, e.g., solvation, temperature, pressure, and electrolytes. ,,, Excitation to a CTTS state can lead to the formation of solvated electrons with a high quantum yield; , the high sensitivity to the local environment and large extinction coefficients of CTTS transitions make them excellent probes of anion solvation dynamics in complex systems.…”

“…Although the lowest-energy CTTS transition has been studied extensively using linear absorption spectroscopy, very little is known about the character of the higher-lying CTTS states of aqueous iodide because of their overlapping nature and the onset of the lowest-lying water electronic absorption (∼6.4 eV). The latter increasingly interferes with the shorter wavelength region of the 1PA spectra . Herein, we present aqueous iodide CTTS spectra measured with interface-sensitive femtosecond broadband deep-UV electronic sum frequency generation (DUV-ESFG) spectroscopy and bulk-sensitive two-photon absorption (2PA) spectroscopy and discuss the salient selection rules and symmetry arguments within a Rydberg transition model to provide insight into the aqueous iodide CTTS spectrum, specifically in the region of overlapping transitions.…”

“…(c) Close-ups of the 1PA and 2PA spectra of aqueous iodide in the region of the higher-energy CTTS transition clearly showing the shift in the peak position. The 1PA spectrum is reproduced from ref measured at 298 K and 250 bar.…”