V.B. Morozov

CARS diagnostics of molecular media under nanoporous confinement

The CARS spectroscopy is used for the diagnostics of carbon dioxide in a nanoporous glass at temperatures ranging from room temperature (20.5°C) to the subcritical temperature (30.5°C) in the pressure range below the saturated-vapor pressure. The contributions of the gas-phase molecules, the molecular layer adsorbed from the gas phase on the pore surface, the condensed liquid-like phase, and the liquid interface in the vicinity of the pore surface can be selected using the analysis of the nonlinear spectral response. The spectral behavior of the carbon dioxide confined in nanopores at the subcritical temperature indicates a state that is similar to the supercritical fluid. This corresponds to a low-temperature shift of the critical point of the medium confined in nanopores.

High resolution study of 1388 cm-1 CO2 vibration by time-domain CARS: spectral exchange and Dicke effect

Abstract The dephasing kinetics of the higher frequency component of the Fermi-resonance dyad ν 1 /2ν 2 (1388 cm −1 ) of CO 2 was studied by means of time-domain CARS in the density range where spectral exchange and Dicke effect play a noticeable role. The spectral exchange manifests itself in the gradual shift to longer delay times of minima and maxima of the beats between different Q -branch components with increasing densities and in the simultaneous beats smoothing. As a result of both the effects, the pulse response was practically exponential at CO 2 densities ⩾ 0.4 Amagat.

Phase Behavior of the Molecular Medium in Nanopores and Vibrational Spectra Structure Transformation

A model description of molecular medium spectra during phase transitions in cylindrical nanopores is developed based on the thermodynamic concept of surface adsorption and capillary condensation. Good agreement of the calculated and experimental spectra measured during carbon dioxide adsorption and condensation in pores of nanoporous Vycor glass with a diameter of 2 nm is obtained. The constructed model connects the behavior of the medium spectra with the characteristics of the porous structure of a material and can be used for their determination based on spectroscopic data.

Narrowing of the Vibrational Spectrum under Compression of Liquid Carbon Dioxide

The broadening and shift of the Q bands of the 1388/1285-cm−1 Fermi doublet of carbon dioxide have been measured by means of the spectroscopy of coherent anti-Stokes Raman scattering in a wide density range realized at compression in dense gaseous and liquid states. The spectrum of the low-frequency Q band exhibits an essential narrowing upon the compression of the liquid in the density range of 320–400 amagat from a maximum width of about 2.2 cm−1 to about 1.7 cm−1 determined by elastic dephasing. The observed dependence is connected with the progressive narrowing of the spectral contribution attributed to the collapsed rotational structure.

Time-domain polarization coherent anti-Stokes Raman spectroscopy of Tl atoms: dephasing measurements of separate multipole moments

Polarization nondegenerate nonstationary coherent anti-Stokes Raman spectroscopy was used in measurements of pulse responses for separate electronic multipole moments. The 6P(1/2)-6P(3/2) transition of Tl atoms was investigated. Doppler dephasing conditions, quantum beats of the hyperfine components of this transition are clearly seen when pure anisotropic scattering is registered, but they are small in the case of purely antisymmetric scattering. Under collisional dephasing conditions the relaxation rates of anisotropic and antisymmetric scattering agree with existing theory within +/-5%.

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 Psat. When pressure was increased above 0.8 Psat, 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 Psat, 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.

Synthesis and characterization of silver nanoparticles in a nanoporous glass

We obtained a metal-dielectric composite by thermal restoration of silver atoms from an alcohol solution of a precursor in nanoporous glass with pores with a radius of 2 nm. The concentration, size, and asphericity degree of metal nanoparticles formed in the pores are characterized according to the measured extinction spectra of the material.

Induction-resonance energy transfer between the terbium-binding peptide and the red fluorescent proteins DsRed2 and TagRFP

Two novel FRET-pairs: Tb3+-binding peptide-DsRed2 and Tb3+-binding peptide-TagRFP have been produced based on the terbium-binding peptide and the red fluorescent proteins DsRed2 and TagRFP. Two induction-resonance energy transfer processes in both FRET-pairs have been registered, from tryptophan of the terbium-binding peptide to Tb3+ and from sensitized Tb3+ to the acceptor, the chromophore, DsRed2 or TagRFP. The lifetimes of terbium in the presence and absence of the acceptor have been determined. It has been shown that the lifetime of Tb3+ in the presence of 150 mM NaCl decreases in both FRET-pairs. The efficiency of fluorescent resonance transfer from Tb3+ to the acceptor proteins is 28 and 35% for Tb3+-binding peptide-DsRed2 and Tb3+-binding peptide-TagRFP, respectively.

Spectral Characteristics of Subcritical Carbon Dioxide in Nanopores

Coherent anti-Stokes Raman scattering spectra measured within the Q-branch of the vibrational transition ν1 are used to gain insights into the state of carbon dioxide molecules in nanopores of Vycor™ glass at room temperature (20.5°C) and a subcritical temperature of 30.5°C and gas pressures up to the saturation point Psat for each temperature. Along with the main spectral component, belonging to gaseous CO2 molecules, the spectra recorded at pressures close to Psat feature a second (low-frequency) component. The second component is associated with the contribution from the CO2 molecules trapped inside pores. A spectral deconvolution with account for the interference of these two bands makes it possible to estimate the spectral characteristics of the second (low-frequency) component at each temperature. At 20.5°C, the bandwidth of the low-frequency component decreases with CO2 pressure, a behavior that can be explained by the transition of CO2 from the adsorbed to the condensed state in the pore. At the subcritical temperature of 30.5°C, the spectral width of the second component is pressure-independent and close to the value measured in the bulk of the supercritical fluid, a result likely associated with a low-temperature shift of the critical point of the substance trapped in nanopores.

Optical nutation at a Raman-active transition

Optical nutation at the Raman-active transition 6P1/2−6P3/2 of thallium atoms (ωR/2πc=7793 cm −1) under resonant Raman excitation by a biharmonic picosecond pulsed field, giving rise to substantial motion of the population, is detected. Optical nutation appears as an oscillatory behavior of the energy of the anti-Stokes scattering of probe pulses, which follow with a fixed delay, as a function of the product of the energies of the excitation pulses. As a result of the dynamic Stark effect, which decreases the frequency of the transition under study, resonance excitation conditions are satisfied for negative initial detunings of the Raman excitation frequency from resonance. The Raman scattering cross section for the transition under study is estimated by comparing the experimental data with the calculations.