Interpretation of the pressure-induced Raman frequency shift of the ν₁ stretching bands of CH₄ and N₂ within CH₄–CO₂, N₂–CO₂ and CH₄–N₂ binary mixtures

Abstract

The pressure-induced frequency shift of the CH4 and N2 bands is interpreted by quantitatively attributing to the attractive and repulsive solvation mean-force variation using the Lennard–Jones 6-12 potential and the perturbed hard-sphere fluid model.

Tracking carbon dioxide adsorbate intramolecular dynamics in pure silica zeolite Silicalite-1 by in situ Raman scattering

“…40 In Zn 2 (bdc) 2 (bpee) MOF, where bpdc = 4,4′-biphenyl dicarboxylate and bpee = 1,2-bis(4-pyridyl)ethylene, the computed binding energy of CO 2 in the pore interiors is much lower, 34 kJ mol −1 , suggesting weaker host–guest interactions, yet the same feature, somewhat contraintuitively, was seen at an even lower energy of 1377 cm −1 . 41 When CO 2 was adsorbed near the coordinatively unsaturated Mg( ii ) centres of MOF-74-Mg (CPO-27-Mg), with an isosteric heat of adsorption in the range 45–50 kJ mol −1 CO 2 , the symmetric stretch was again found alone at 1382 cm −1 , 42 notably at the same frequency as for the Ni-analogue of the same material, 36 and only 6 cm −1 red-shifted from the gas-phase value. These observations indicate that the symmetric stretch mode of the molecule alone is rather insensitive to small variations in the local intermolecular interactions or may suggest that there are inconsistencies in the measurements in different laboratories and experimental setups.…”

“…Consequently, useful polynomial interpolations have been derived from extended pressure and temperatures ranges, relating this splitting to the CO 2 density in the gas, liquid, and solid phases, below and above the critical temperature. [28][29][30][31][32][33][34] Based on these data, accurate contactless remote CO 2 pressure [31][32][33][34][35][36][37][38][39] sensing in pure and inclusion phases as well as temperature and salinity sensing methods have been devised. 34 However, despite the urgent need for new CO 2 -storage technologies and materials, and the clear usefulness of Raman spectroscopy, experimental Raman studies on micropore-confined CO 2 phases/adsorbates are rather scarce.…”