Multiple photon excitation of polyatomic molecules from the many rotational states by an intense pulse of IR radiation

The investigation of the role of pulse duration in the absorption of CO₂ laser pulses by polyatomic molecules has shown that the rotational relaxation does not contribute significantly to the absorption of intense IR radiation. This proves the existence of purely radiative depletion of all rotational states in monochromatic fields of moderate intensity.     

Optical spectroscopy of the Eu(FOD)<Subscript>3</Subscript> complex impregnated into the free volume of nanoporous glass and polymethylmethacrylate using supercritical carbon dioxide

The absorption and photoluminescence spectra of Eu(FOD)₃ molecules (FOD = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) impregnated into samples of nanoporous Vycor glass and polymethylmethacrylate using supercritical carbon dioxide were measured. The influence of the matrix on the shape and intensity of the absorption bands of Eu(FOD)₃ molecules and the photoluminescence bands of Eu³⁺ ions was analyzed.     

Quantifying uncertainty in the measurement of arsenic in suspended particulate matter by Atomic Absorption Spectrometry with hydride generator

Arsenic is the toxic element, which creates several problems in human being specially when inhaled through air. So the accurate and precise measurement of arsenic in suspended particulate matter (SPM) is of prime importance as it gives information about the level of toxicity in the environment, and preventive measures could be taken in the effective areas. Quality assurance is equally important in the measurement of arsenic in SPM samples before making any decision. The quality and reliability of the data of such volatile elements depends upon the measurement of uncertainty of each step involved from sampling to analysis. The analytical results quantifying uncertainty gives a measure of the confidence level of the concerned laboratory. So the main objective of this study was to determine arsenic content in SPM samples with uncertainty budget and to find out various potential sources of uncertainty, which affects the results. Keeping these facts, we have selected seven diverse sites of Delhi (National Capital of India) for quantification of arsenic content in SPM samples with uncertainty budget following sampling by HVS to analysis by Atomic Absorption Spectrometer-Hydride Generator (AAS-HG). In the measurement of arsenic in SPM samples so many steps are involved from sampling to final result and we have considered various potential sources of uncertainties. The calculation of uncertainty is based on ISO/IEC17025: 2005 document and EURACHEM guideline. It has been found that the final results mostly depend on the uncertainty in measurement mainly due to repeatability, final volume prepared for analysis, weighing balance and sampling by HVS. After the analysis of data of seven diverse sites of Delhi, it has been concluded that during the period from 31^st Jan. 2008 to 7^th Feb. 2008 the arsenic concentration varies from 1.44 ± 0.25 to 5.58 ± 0.55 ng/m³ with 95% confidence level (k = 2).     

Influence of Hydrodynamic Processes Generated by 1.94-μm Pulsed Laser Radiation on Daphnia magna Crustaceans

Acoustical Physics - The hydrodynamic processes occurring in water under the action of pulsed laser radiation with a power of 20 W, wavelength of 1.94 μm, and a pulse duration of 100 ns were...     

Photo–induced processes in Ag and Eu β-diketonates incorporated into aerogel matrix of silicon dioxide by supercritical fluid impregnation

Samples of silicon dioxide aerogel with embedded Ag and Eu β-diketonate molecules are obtained by impregnation in supercritical carbon dioxide (SC-CO₂). The sample impregnated by Eu(tta)₃ molecules possesses photoluminescence properties. Moreover, adsorption of Eu(tta)₃ on the walls of the pores results in a strong broadening of the Stark components of its photoluminescence spectra. It is found that aerogel impregnation by AgFOD molecules followed by laser irradiation causes the formation of Ag nanoparticles in the sample volume as a result of AgFOD photolysis and subsequent diffusion self-assembly. The Ag nanoparticles assemble into filament structures due to self-organization as they focus laser radiation.     

Broadening of vibrational spectra of carbon dioxide upon absorption and condensation in nanopores

Coherent anti-Stokes Raman Spectroscopy (CARS) has been used to study the vibrational Q-branch with the frequency of 1388 cm^?1 of the ν₁ mode of carbon dioxide molecules filling a sample made of nanopore glass at room temperature (20.5°C). The measurements were carried out in a gas cell at pressures approaching saturation P _sat. When pressure was increased above 0.8 P _sat, in addition to the spectral component due to the gaseous phase molecules, the CARS spectra featured a component due to the molecules adsorbed on the pore walls. Simulation of spectra taking the interference of these two contributions into account enabled the estimation of the broadening of the vibrational molecular spectra in the adsorbed layer. The spectral width of the component due to the adsorbed molecules was nearly a factor of two times larger than that of molecules in the bulk liquid phase. At pressures above 0.94 P _sat, the spectral width of the component due to the adsorbed molecules decreased to values close to those measured in the bulk liquid phase, which corresponds to the condensation of molecules in nanopores.     

Optoacoustic detection of multiple photon molecular absorption in a strong IR field

A new method based on the optoacoustic effect has been proposed to measure multiple photon absorption at vibrational molecular transitions in a strong IR laser field. Comparison measurements of the average absorbed energy have been done by this method for molecules with different dissociation limits in a strong CO₂-laser field, the field intensity changed therewith by four orders. For the poly-atomic molecules C₂H₄ and SF₆ having a comparatively low dissociation limit, the absorption increases monotonously as the power density of laser radiation P increases up to the dissociation limit. For three-atom molecules, such as D₂O and OCS, absorption saturation takes place with P ? 10 MW/cm².     

Attenuation and speckle modulation of laser light in dispersive dye-doped media: Competition of absorption and scattering processes

The effect of competition of laser light absorption and scattering in dispersive media (1 μm polystyrene microspheres in ethylene glycol) with added dye (rhodamine 6G) was studied under the condition of near-resonant absorption of probe light in the host medium (solution of rhodamine 6G in ethylene glycol). The parameters of speckle modulation of transmitted light (the average speckle intensity and the oscillation index) were applied for characterization of light transport in the probed scattering systems as a function of dye concentration. The increase in dye concentration does not cause the expected decay in the transmittance of the examined dispersive systems for 532 nm laser light, but results in the decrease of their turbidity. This effect is accompanied by the rise of the average intensity and the oscillation index of speckle-modulated light, and can be rationalized by partial matching of the real parts of refractive indices for the host medium and embedded scatterers. This interpretation was supported by statistical modeling of light transport through the examined scattering systems.     

Methods for studying the coherent 4D structural dynamics of free molecules and condensed state of matter

Studies in the coupled 4D spatial and temporal continuum are necessary for understanding the dynamic features of molecular systems with a complex profile of the potential energy surface. The introduction of time sweep into diffraction methods and the development of principles for studying coherent processes have revealed new approaches to the analysis of the dynamics of wave packets, the intermediate products and the transition state of the reaction center, and short-lived compounds in gaseous and condensed media. The use of picosecond and femtosecond electron probe pulses, synchronized with excitation laser pulses, determined the development of ultrafast electron crystallography, time-resolved X-ray diffraction, and dynamic transmission electron microscopy (DTEM). One of the most promising applications of the developed diffraction methods is the characterization and visualization of the processes occurring upon the photoexcitation of free molecules and biological objects and the analysis of surface and thin films. The whole set of spectral and diffraction methods based on different physical principles, which are complementary and make it possible to perform the photoexcitation of nuclei and electrons and carry out diagnostics of their dynamics at ultrashort time sequences, reveal new possibilities for studies with the necessary integration of the “structure-dynamics-function” triad in chemistry, biology, and materials science.     

Selective modification of polylactide by introducing acrylate groups: IR spectroscopy,gel permeation chromatography,and differential thermal analysis

One-stage modification of polylactide has been performed to obtain the acrylate derivatives of the polymer capable of further polymerization and preparation of cross-linked polymer materials suitable for creating implants. The reaction mechanism was determined by IR spectroscopy, gel permeation chromatography, and differential thermal analysis. It was shown for the first time that the reaction path changes depending on the ratio of components so that the desired product polylactide acrylate forms with a ~90% yield only in the presence of large (approximately tenfold) excesses of the isocyanate and acrylate components; at the equimolar ratio of components generally used in urethane formation, a mixture of the desired product (~30%), oligourethane diacrylates, and unchanged polylactide forms.