Estimation of the Absorption Cross Section of the Forbidden Vibrational Band of Hydrogen in Nanoporous Aerogel
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ECTROSCOPY OF AMBIENT MEDIUM
Estimation of the Absorption Cross Section of the Forbidden Vibrational Band of Hydrogen in Nanoporous Aerogel B. G. Ageeva, * and Yu. N. Ponomareva, ** a
V.E. Zuev Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, Tomsk, 634055 Russia *e-mail: [email protected] **e-mail: [email protected] Received December 9, 2019; revised December 9, 2019; accepted December 23, 2019
Abstract—Measurement results of the concentration of H2 molecules into aerogel (SiO2) nanopores with diameter 20 nm are presented. The standard gasometric method is used. The experimental data on H2 molecule concentration together with the data on integral intensity of collision-induced H2 absorption 0–1 band are used for estimation of the absorption cross section at the band maximum. Keywords: absorption, aerogel, nanopore, hydrogen, gasometric, absorption DOI: 10.1134/S102485602004003X
INTRODUCTION The studies of the absorption spectra of molecular gases in optically transparent nanoporous materials with the nanopore diameter of 5–50 nm show the decisive effect of the collisions of molecules with nanopore walls on the profiles, broadening and shifts of spectral lines, and induced absorption at forbidden vibrational transitions of symmetric molecules such as H2 [1–5]. The authors of [5] consider the appearance of the forbidden absorption band of molecular hydrogen confined in aerogel nanopores as a result of collisions of H2 molecules with nanopore walls and the possible contribution of a layer of molecules adsorbed. The concentrations of those and other molecules were not estimated. This work is aimed at gasometric measurements of the concentration of gas-phase hydrogen molecules in SiO2 nanopores and estimation of the absorption cross section at the maximum of the hydrogen 0–1 vibrational band induced by collisions of molecules with nanopore walls under the experimental conditions [5].
We used an aerogel parallelepiped of 27.3 cm3 in volume with a density of 0.25 g/cm3 and an average pore size of 20 nm as a sample. We applied the standard vacuum technique and a version of the gasometric method (Fig. 1) which is widely used in different fields of science and technology (see, for example, [7, 8]). First, gas adsorption was studied in a vacuum system. Air was pumped out of the system with an exposure chamber (0.5 L in volume) to a residual pressure of ∼10−1 Torr, after which it was filled with pure H2 at atmospheric pressure at the time of measurement, to exclude gas exchange between the internal volume of the vacuum system and the ambient air due to possible uncontrolled leaks. After that, a change in pressure in the vacuum system connected to an exposure chamber was recorded for 4 h. This time is required because the gas pressure (even for H2O vapor) in a chamber with an aerogel stabilizes after 4 h [9].
MEASUREMENT OF THE CONCENTRATION OF H2 ADSORBED BY A SiO2 AEROGEL SAMPLE SiO2 aerogel is a highly porous (porosity can be 80–99%) light substance transparent in the visible and IR spectral regions
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