A new angle into time-resolved photoacoustic spectroscopy: A layered prism cell increases experimental flexibility

Abstract

A new pulsed photoacoustic calorimetry cell that uses transmission of light through a pair of dovetail prisms is discussed. The layered prism cell (LPC) combines the enhanced time-resolution capabilities of the “layered” front-face irradiation geometry with the zero-background and broadband flexibility of the classical cuvette geometry. This work provides a phenomenological description of photoinduced pressure changes to yield an analytical expression to calculate the magnitude of the photoinduced acoustic pressure wave in a series of solvents. The mechanical to electrical conversion efficiency for an ultrasonic transducer coupled to the LPC is presented to provide a comparison of the experimentally observed photoinduced acoustic signal amplitudes to the empirically calculated acoustic signal amplitudes. An analysis of the background signals due to absorption and electrostriction of the media provides insight into the issues of sensitivity and limitations of pulsed photoacoustic experiments. The LPC provides several benefits to increase the flexibility of the photoacoustic spectroscopy: (1) greater sensitivity, (2) enhanced time resolution, and (3) the ability to obtain kinetic data in complex solvent mixtures. Under optically dilute conditions in the layered cell geometry, the acoustic transient time, τa, approaches zero because the photoinduced acoustic wave homogeneously expands against the walls of the photoacoustic cell. To demonstrate the unique capabilities of the LPC, rates of hydrogen abstraction by tert-butoxyl radical from solvent mixtures containing ethyl and methyl alcohol are presented.

Optothermoacoustic Phenomena in Highly Diluted Suspensions of Gold Nanoparticles

“…Therefore, high temporal resolution is the most salient characteristic of this kind of OA detection method. In the past, several groups developed optoacoustic sensors with nanosecond resolution operating in the backward mode (front-surface transducers, FST) [10][11][12][13][14]. In the present paper we report results of studies of photothermoacoustic processes taking place in a thin layer of an ultra-diluted suspension of gold nanoparticles (NP) with the use of a wide-band FST sensor.…”

Time‐resolved photoacoustic calorimetry as a tool to determine rate constants of hydrogen‐abstraction reactions

“…Since the solutions used are normally very dilute, it is generally assumed that both will have χ equal to that of the pure solvent. For instance, in methanol, this assumption is not valid [37]. However, using benzene, iso-octane, carbon tetrachloride, and acetonitrile as solvents, the shape and time of arrival of the photoacoustic waveform is the same for calibration and experiment, and increasing the amount of peroxide in the sample solution does not noticeably affect the time of arrival of the photoacoustic waveform.…”

Photoacoustic characterization of protein dynamics following CO photodetachment from fully reduced bovine cytochrome c oxidase

“…See Section 2 for definition of thermodynamic parameters and Section 4 for further details concerning assumptions regarding DH 1 . each temperature at the same time that the signal from the sample dissolved in buffer was measured [28][29][30][31][32][33][34].…”

“…Subsequent to photon absorption, the absorber must release energy. In solutions, this produces volume changes due to many processes, including heat released to solvent, conformational change of the chromophore, electrostriction caused by solvent redistribution to accommodate the release or uptake of ions [30][31][32][33], and electrostriction in response to the electric field of the incident photons [34]. The volume changes give rise to a photoacoustic signal which can be deconvoluted to reveal component lifetimes that correspond to the responsible molecular events.…”