Showing papers on "Photoacoustic spectroscopy published in 1985"
TL;DR: In this paper, the authors explore the modes of photoacoustic signal generation from highly porous powders and show that the thermal and pressure modes of signal generation are important, while the volumetric expansion of the interstitial gas in the porous sample is less important.
Abstract: Model calculations and experiments have been performed to explore the modes of photoacoustic signal generation from highly porous powders. These indicate that two modes of signal generation are important: (i) a thermal mode resulting from heating of the sample and conduction to the transducer gas above the sample, and (ii) a pressure mode resulting from the volumetric expansion of the interstitial gas in the porous sample. For highly porous materials, such as silica, the pressure mode can dominate the photoacoustic signal. Under conditions where the pressure mode is dominant, the frequency dependence of the acoustic magnitude and phase is similar to that of a homogeneous sample in photoacoustic saturation, however, the photoacoustic signal will still scale with absorption coefficient in this regime. The pressure mode of signal generation can be attenuated by compaction of the powdered sample to reduce the porosity. Unambiguous determination of photoacoustic saturation is shown to require measurements as f...
56 citations
43 citations
TL;DR: Simultaneous photoacoustic spectroscopy is introduced as a convenient and accurate method for the measurement of small absorption line shifts due to the pressure of the surrounding atmosphere in this article, where rather large pressure shift coefficients of up to −0.040 cm−1/atm are observed, which have to be taken into consideration in remote sensing applications in which the exact positioning on the line center is critical.
Abstract: Simultaneous photoacoustic spectroscopy is introduced as a convenient and accurate method for the measurement of small absorption line shifts due to the pressure of the surrounding atmosphere. Results are presented for fourteen water vapor lines in the 725-nm spectral region. Rather large pressure shift coefficients of up to −0.040 cm−1/atm are observed, which have to be taken into consideration in remote sensing applications in which the exact positioning on the line center is critical, e.g., differential absorption lidar.
34 citations
TL;DR: It is shown that very concentrated dried rod outer segment membranes have a sufficient thermal diffusivity to be analyzed by photoacoustic spectroscopy, and the low temperature dissipation spectrum has been obtained.
Abstract: — Photoacoustic spectroscopy is used to investigate the uptake of energy in the primary photoreaction of bovine visual pigment (Rhodopsin → Bathorhodopsin). It is shown that very concentrated dried rod outer segment membranes have a sufficient thermal diffusivity to be analyzed by this technique. From the photoacoustic and absorption spectra of these membranes, the low temperature dissipation spectrum has been obtained and the results are consistent with the storage of 145 kJ mol-1 in the primary event of vision having a quantum yield of 0.67. By photoacoustic spectroscopy, this process is continuously monitored from 350 to 550 nm and its efficiency is found to vary by less than 10%, even in the spectral region of the β-band of rhodopsin.
32 citations
30 citations
TL;DR: Teflon coating is found to provide the resonant photoacoustic cell with accurate real time response for both hydrazine and ammonia sample flows.
Abstract: A photoacoustic signal rise time technique is used to evaluate the suitability of several surface materials for minimizing sample adsorption loss in a trace level toxic vapor monitor. Four materials, 304 stainless steel, gold, paraffin wax, and Teflon, are tested using ammonia as a sample. Teflon is also tested using hydrazine. Results show that both metals interact strongly with the sample. Teflon coating is found to provide the resonant photoacoustic cell with accurate real time response for both hydrazine and ammonia sample flows.
29 citations
01 Jan 1985
26 citations
TL;DR: In this paper, a highly polarizable inert gas, xenon, was used to enhance the surface modes which are preferentially oriented parallel to the surface and suppress the intensity of the perpendicular modes.
Abstract: Fourier transform infrared photoacoustic spectroscopy has been used for the analysis of surface functionality and adsorbed species. Using a highly polarizable gas in the photoacoustic cell and comparing the spectra with a nonpolarizable coupling gas, one can obtain useful information regarding the species present and their orientation with respect to the surface. A highly polarizable inert gas, xenon, enhances those surface modes which are preferentially oriented parallel to the surface and suppresses the intensity of the perpendicular modes. The two types of modes for adsorbed molecules on the oxide surfaces such as silica have been demonstrated. The intensities of the carbon monoxide mode (parallel to the surface) are greatly enhanced and those of adsorbed water (perpendicular) are suppressed. Surface hydroxyls show less intensity in xenon than helium, reflecting preferentially perpendicular orientation with respect to the surface. This method requires only a routine photoacoustic setup and the use of polarizable and nonpolarizable gases.
24 citations
01 Mar 1985
TL;DR: In this paper, the potential of photoacoustic spectroscopy (PAS) for the study of marine organic films has been assessed, and it is shown that PAS can be used at the solid/liquid interface to detect the presence of a primary bacterial film formed from seawater.
Abstract: The potential of photoacoustic spectroscopy (PAS) for the study of marine organic films has been assessed. It is shown that PAS can be used at the solid/liquid interface to detect the presence of a primary bacterial film formed from seawater. Data for several types of organic films on Parafilm are presented. Data can be obtained in situ as the film is forming under water, or subsequent to film formation on the dried film. The technique is especially useful for detecting organic films on surfaces that are neither optically reflective nor transparent. It is concluded that further development of the technique is warranted to complement existing thin film analysis methods often requiring reflectivity or transparency or both and to increase the signal-to-noise ratio of data from the water cell so that PAS can be used to distinguish various components of a seawater organic film.
22 citations
TL;DR: In this article, photoacoustic spectroscopy has become a widely used spectroscopic tool for the investigation of the thermal and optical properties of a wide variety of samples, and in probing nonradiative deexcitations that follow a variety of excitations in matter.
Abstract: During the past decade, photoacoustic spectroscopy has become a widely used spectroscopic tool. It has proved to be valuable in the investigation of the thermal and optical properties of a wide variety of samples, and in probing nonradiative deexcitations that follow a variety of excitations in matter.
21 citations
TL;DR: Fourier transform infrared photoacoustic spectroscopy was applied to the nondestructive detection of subsurface layer of bilayered films in this paper, which was carried out by the application of the subtraction technique to the photo-acoustic amplitude spectra of bilayers whose top layer has various values in thickness.
Abstract: Fourier transform infrared photoacoustic spectroscopy was applied to the nondestructive detection of subsurface layer of bilayered films Spectral separation of the subsurface layer was carried out by the application of the subtraction technique to the photoacoustic amplitude spectra of bilayered films whose top layer has various values in thickness As a result, it was found that the spectrum corresponding to the subsurface layer could be separated, and that the photoacoustic depth profiling was possible as far as the depth, which is approximately half the value of the thermal diffusion length
Patent•
16 Jul 1985TL;DR: In this paper, a method and an apparatus for the detection of thermo-optical signals are described, where the heat waves, as a result of the absorption of an amplitude-modulated light beam, are not detected by an acoustic recorder, as in the case of photoacoustic spectroscopy, but rather optically.
Abstract: Both a method and an apparatus for the detection of thermo-optical signals are disclosed. There is involved a method related to photoacoustic spectroscopy (PAS) in which the heat waves, as a result of the absorption of an amplitude-modulated light beam, are not detected by an acoustic recorder, as in the case of photoacoustic spectroscopy, but rather optically. For this purpose, a second beam of light is conducted over the surface of the specimen and the influence exerted thereon by periodic variations in index of refraction which are dependent on temperature or pressure is measured. For the guiding of the measurement beam a so-called ATR plate known from ATR (attenuated total reflection) spectroscopy is used, it being placed as cover glass over the specimen. Within this plate the measurement light is guided in the vicinity of the critical angle for total reflection at the plate/specimen interface. Changes in index of refraction at the interface as a result of the absorption of the excitation light lead to a detectable modulation of the intensity of the measurement light.
TL;DR: In this article, the authors used a He-Ne laser exciting beam to probe commercially available, powdered and pressed nickel electrodes with dual-porosity profiles and found that these electrodes behave photoacoustically approximately like a simple continuous composite-layer solid.
Abstract: Frequency-domain Photoacoustic Spectroscopy (PAS) was used with a He-Ne laser exciting beam to probe commercially available, powdered and pressed nickel electrodes with dual-porosity profiles. The frequency response of the electrodes was shown to be capable of providing quantitative information about the thermal conductivity and diffusivity of each of the two porous layers, provided the depth of the porosity junction in the electrode bulk is known. The reasonable agreement of the experimental data with a one-dimensional mathematical model of the photoacoustic response from a two-layer, photoacoustically saturated, continuous system indicates that powdered and pressed nickel electrodes behave photoacoustically approximately like a simple continuous composite-layer solid. This conclusion, together with experimental PAS results from uniporous electrodes, emphasizes the high potential of photoacoustic spectroscopy as a nondestructive, depth profiling, analytical technique for the determination of complex porosity profiles in electrodes manufactured for use in electrochemical energy conversion devices, such as fuel cells.
TL;DR: In this article, photoacoustic measurements of biological materials such as DNA, lysozyme, squalene and yeast cells were performed for the first time in the vacuum-UV region above 150 nm using the gas-microphone technique and synchrotron radiation as a light source.
Abstract: — Photoacoustic measurements of biological materials such as DNA, lysozyme, squalene and yeast cells were performed for the first time in the vacuum-UV region above 150 nm using the gas-microphone technique and synchrotron radiation as a light source. The samples studied were in a form of thin film supported on a self-supporting collodion film. The results obtained for the phase of the photoacoustic signal were found consistent with the predictions from the simple one-dimensional theory. The signal amplitudes obtained as a function of the incident wavelength were interpreted as giving the absorptance (the fraction of the incident photon energy dissipated in the sample) spectrum.
TL;DR: In this paper, a photoacoustic spectrometer using an open-ended cell has been developed for thein vivo measurements of cutaneous optical absorption, which is very flexible because it uses an ultraviolet silica light guide and double-sided adhesive tape, which ensures satisfactory contact between the cell and the skin.
Abstract: A photoacoustic spectrometer using an open-ended cell has been developed for thein vivo measurements of cutaneous optical absorption. This detector is very flexible because it uses an ultraviolet silica light guide and double-sided adhesive tape, which ensures satisfactory contact between the cell and the skin. The noise produced by skin vibrations has been considerably reduced by choosing a differential microphone assembled in between two identical cells, only one of which is illuminated. The characteristics of the photoacoustic detector are given in terms of the sensitivity-to-noise ratio. The observed performance enables us to consider various original applications of photoacoustic spectroscopy. The first experimental results were obtained fromin vivo measurements on volunteers: the optical absorption spectra of the skin and topically applied drugs are presented. The advantages and inherent limitations of this type of investigation are demonstrated in this paper, and possible solutions are discussed.
TL;DR: In this article, the wave equation in which the source term is coupled with the thermal energy migration was analyzed, and the physical meaning of the phase of photoacoustic signals generated in turbid solutions was clarified.
Abstract: The wave equation in which the source term is coupled with the thermal energy migration was analyzed, and the physical meaning of the phase of photoacoustic signals generated in turbid solutions was clarified. These theoretical results, partially verified by experiments, showed the possibility for novel thermal characterizations and size measurement methods of microparticles. The theoretical limitation of the size measurement was 102 A for samples with nonradiative relaxation times of 1 nsec.
TL;DR: Measurements are reported of absorption coefficient for nitrogen-diluted propane obtained by both photoacoustic spectroscopy and photothermal deflection spectroscopic using a CO/sub 2/ laser.
Abstract: Measurements are reported of absorption coefficient for nitrogen-diluted propane obtained by both photoacoustic spectroscopy and photothermal deflection spectroscopy using a CO/sub 2/ laser.
TL;DR: A new highly sensitive method of trace detection using both chemical amplification and quenching of the optoacoustic effect is reported.
Abstract: In contrast to excitation in the infrared, generation of the optoacoustic effect in the visible or ultraviolet region of the spectrum opens up the possibility of initiation of chemical reactions such that the energy released by the reactions far exceeds the amount of energy absorbed from the light beam. Since the magnitude of the optoacoustic effect is proportional to the amount of heat liberated by the chain reaction, the effect of the addition of a radical scavenger is to quench the chemical liberation of heat in the spectrophone and hence to decrease the acoustic signal amplitude. A new highly sensitive method of trace detection using both chemical amplification and quenching of the optoacoustic effect is reported. 22 references, 3 figures, 1 table.
TL;DR: In this paper, a variable temperature cryogenic photoacoustic detector has been developed for making spectroscopic measurements on gas phase molecules, and temperatures in the range of 77-300 K are obtained with this device.
Abstract: A variable temperature cryogenic photoacoustic detector has been developed for making spectroscopic measurements on gas phase molecules. Temperatures in the range of 77–300 K are obtained with this device.
TL;DR: In this article, photoacoustic and absorption spectra of single crystals of GaSe at room temperature were studied in the neighborhood of the intrinsic absorption edge, and the formation of excitons was observed.
Abstract: Photoacoustic and absorption spectra of single crystals of GaSe at room temperature have been studied in the neighborhood of the intrinsic absorption edge. Analysis of the spectra showed formation of excitons. This is the first time that the exciton effect has been observed with photoacoustic spectroscopy.
01 Jan 1985
TL;DR: In this article, photoacoustic (PAS) and photothermal methods are based on the measurement of the heat generated by the radiationless processes for deactivation of excited species.
Abstract: Photoacoustic (PAS) and photothermal methods are based on the measurement of the heat generated by the radiationless processes for deactivation of excited species [1–5]. These methods are complementary to other photophysical and photochemical methods and, in addition, some of them permit the measurement of heat dissipation in non-transparent or highly scattering media, e. g., in living tissues [6] or in adsorbed substances [7].
TL;DR: In this paper, the infrared photoacoustic spectra were obtained from organic films on inorganic particulate adsorbents and the detection sensitivity was estimated to be 0.2 monolayers of an adsorbed organic compound.
Abstract: Infrared photoacoustic spectra were obtained from organic films on inorganic particulate adsorbents. Under favorable conditions, including strong absorption bands and high surface area silica and alumina substrates, the detection sensitivity of photoacoustic spectroscopy is estimated to be 0.2 monolayers of an adsorbed organic compound. Because of the molecular information provided by IR spectroscopy, reactions of adsorbed organic compounds may be examined in situ. Examples shown involve photochemical reactions of sorbed polynuclear aromatic compounds that are potentially important in the atmospheric chemistry of combustion generated aerosols. 21 references, 7 figures.
TL;DR: In this paper, the phase angle φ of a gas-coupled photoacoustic (PA) signal has been measured as a function of coupling gas column thickness lg for a one-dimensional PA cell, where the PA signal is excited by a modulated continuous laser beam incident on an opaque solid surface of silicon.
Abstract: The phase angle φ of a gas‐coupled photoacoustic (PA) signal has been measured as a function of coupling gas column thickness lg for a ‘‘one‐dimensional’’ PA cell. The PA signal is excited by a modulated continuous laser beam incident on an opaque solid surface of silicon. We show that the observed data can be explained in a PA model including the consideration of a residual volume in the PA cell, together with the consideration of viscous damping of the PA signal at small lg.
TL;DR: In this article, the Fourier Transform Infrared Photoacoustic Spectroscopy (FT-IR/PAS) was used to obtain optical absorption spectra from strongly scattering and/or opaque materials which are difficult to study by conventional photometric methods.
Abstract: Photoacoustic Spectroscopy (PAS) is now well-established as a useful technique for obtaining optical absorption spectra from strongly scattering and/or opaque materials which are difficult to study by conventional photometric methods. However, its quantitative application to solids in the UV-visible region has been somewhat restricted by the phenomenon of photoacoustic (PA) signal saturation, in which the intensity of the stronger bands in the spectrum becomes insensitive to changes in analyte concentration. By comparison, with the recent advent of Fourier Transform Infrared Photoacoustic Spectroscopy (FT-IR/PAS), this problem is expected to be much less serious in view of the low absorptivities characteristic of IR bands. Indeed, recent work in our laboratory has shown that when NH3 is sorbed stepwise into the bulk of 12-tungstophosphoric acid, H3PW12O40, the base is quantitatively converted to NH4+ ion, and the calibration curve of the analyte peak area (standardized against a reference band of the substrate) vs. analyte concentration is virtually linear up to stoichiometric loading. With the use of this method, several salts of the parent acid were found to exist in partial (Bronsted) acid form, and adjusted molecular formulae thus calculated were consistent with those obtained in dependently by elemental analysis.
TL;DR: The use of photoacoustic spectroscopy in the study of the absorption spectra and thermal kinetics of photochromic reactions in the crystalline and adsorbed states was demonstrated in the following photochemical reactions.
01 Feb 1985
TL;DR: In this paper, the relative energies emitted as fluorescence of cyanine monolayers on glass was estimated by comparing photoacoustic spectra on this substrate with those on silver halide surfaces where dye fluorescence is completely quenched by photoelectron injection into AgBr.
Abstract: Photoacoustic spectra of monolayer assemblies of cyanine dyes on various solid surfaces (glass, laminated and evaporated AgBr layers) have shown that these dye layers show different monomer to dimer ratios on different surfaces. Conclusions concerning the geometrical orientation of cyanine molecules on silver halides as drawn from surface pressure isotherms and absorption spectra were confirmed by photoacoustic spectroscopy. The relative energies emitted as fluorescence of cyanine monolayers on glass was estimated by comparing photoacoustic spectra on this substrate with those on silver halide surfaces where dye fluorescence is completely quenched by photoelectron injection into AgBr. For electron transfer experiments in organized monolayer assemblies containing a cyanine donor and the electron acceptor N,N′-distearylviologen, we concluded from photoacoustic measurements and from fluorescence spectra that mainly radical formation and no thermal deactivation occurred after electron transfer. However, by using a nonfluorescent azo dye acceptor, thermal deactivation was shown to be the dominant process after energy transfer from an excited cyanine donor to the acceptor.
TL;DR: In this article, a small volume multipass cell for photoacoustic detection is presented, whose transversely excited cylindrical cavity allows about 30 passes and the pressure and frequency dependence have been described with a simple model.