V. I. Tikhonov

Sorption experiments with water spin isomers in glycerol

Sorption experiments with water/glycerol solution were performed by measuring the ortho/para content in saturated water vapor using the 1-THz BWO spectral method. The results were interpreted as detection (i) of preferential fugacity of ortho molecules from the glycerol surface and (ii) the ability of glycerol to keep the deviation from 3:1 normal ortho/para water ratio for unexpectedly long time (several weeks for 0.5 % water concentration).

On the possibility of sorting ortho and para water molecules during diffusion in nanopores

The possibility of spatial sorting of ortho and para water molecules at filtering water vapor in a nanoporous medium is justified. Three factors are indicated, which in combination can cause sorting: Knudsen character of motion of molecules in nanopores, inhomogeneous surface electric fields in pores, and water molecule sorting over rotational states in an inhomogeneous electric field, recently implemented in experiments with molecular beams.

Diffusion kinetics of water molecules in a nanoporous adsorbent

The diffusion of water vapor into porous polymer adsorbent MN-200 has been investigated by diode laser spectroscopy with a time resolution of 0.1 s. The cascade character of diffusion, caused presumably by the fractality of the porous matrix space, is established by decomposition analysis. The collisionless (Knudsen) mode of water motion in pores, in which water molecules can be sorted according to their spin states, is selected.

A diode-laser spectrometer for measuring ortho/para composition of water vapor

A diode laser spectrometer, which is ment for recording ortho-and paracomposition of water vapor in gas mixtures, is described. The studied mixture is probed by infrared radiation at frequencies of the resonance absorptions of ortho-and paramolecules of water (λ ≈ 1.85 μ m). The recording rate of spectral ortho-and paralines is 2 Hz, and the ortho/para composition is calculated in real time with respect to their integrated intensities. An accuracy of 1% is ensured in a 0.01- to 20-Torr partial pressure range for water vapor and in a 0- to 700-Torr partial pressure range for the buffer gas.

Deviations from the normal ortho/para ratio for water (3 : 1) in the vapor phase in dynamic sorption

Deviations of the ortho/para ratio from its normal value (3: 1) were observed by spectral selective detection of ortho and para water molecules when water vapor passed through a column with a nanoporous polymeric adsorbent. The effect was suggested to be related to the nonstationary dynamics of sorption, that is, nonequilibrium character of chromatography. In terms of this model, the factor of spin ortho/para selectivity is slow and unequal diffusion of the spin isomers of water molecules inside the adsorbent, a process spurious for ideal equilibrium chromatography.

Cascade diffusion of water molecules in a porous granular medium

Water vapor inleakage to a porous granular adsorbent was studied by diode laser spectroscopy. Stepping in the temporal variation of the diffusivity, probably associated with porous matrix space fractality, was detected. The H2O molecular sensing technique is proposed as a tool for experimental study of the structure of porous media and processes occurring in them.

A laser analyzer of the kinetics of interaction of water molecules with an adsorbent

A device for recording high-speed processes of water-vapor sorption at the surfaces of porous materials is described. The water-vapor pressure over a sample is measured during the sorption process by registering the integral intensity of the absorption line of H2O molecules at a wavelength of 1.85 μm. The kinetic curves of changes in the partial pressure (concentration of H2O molecules) from 1 mTorr to 20 Torr are recorded in a time range from 1 ms to 24 h with an accuracy better than 1% at buffer-gas concentrations of 0–760 Torr. The obtained data are used to determine the sorption and structural parameters of investigated materials.

Precursor effect during water vapor diffusion in a porous medium

In water vapor diffusing through a granular adsorbent layer into vacuum, water molecules overcoming an adsorption column without an appreciable delay as pulses, i.e., precursors of the main front, were detected. This effect is explained by the sluggishness of water molecule diffusion into adsorbent grains and the dependence of the adsorption capacity of molecules on their rotational states via the Stark effect in a surface electric field of an adsorbent.

Kinetics of water vapor diffusion in activated carbon

We describe an experimental method for studying rapid processes of water vapor sorption by fine-dispersed and porous materials. The concentration of gas-phase water molecules is detected during adsorption by a laser-diode spectrometer. The kinetic pressure curves are recorded in a time window of 10−1 to 103 s and are analyzed using analogy of the diffusion flow with the electric current in a branched RC circuit. The proposed model establishes the relation between the kinetics curves being measured and the structural parameters of the medium.

Kinetics of water molecule adsorption on the porous silicon surface

The kinetics of water vapor adsorption on the porous silicon surface is studied by the gas relaxometry method. The process multistepping which is reflected in sequential changes in H2O molecule diffusivities into the porous matrix, is found. Phenomenological models describing the experiment are considered.