Infrared spectra and spinning diffusion of methyl bromide in solutions

Sorption Thermodynamics of CO2, H2O, and CH3OH in a Glassy Polyetherimide: A Molecular Perspective

“…Similar band profiles were reported in the literature (i.e., a broad Gaussian component superimposed onto a sharper peak of larger intensity) and were interpreted assuming the Gaussian part as being a remnant of the gas-phase spectrum, while the sharp, Lorentz-like component was interpreted as the purely vibrational transition active in the condensed phase (but not in the gas-phase) [73,74]. According to this interpretation, the two-component band-shape was the consequence of probe dynamics within the molecular environment (essentially free rotation in the early stages of the relaxation process, 0.2–1.0 ps), which produced the Gaussian part, and a random rotational diffusion regime at later stages (the so-called Debye regime), giving rise to the Lorentzian part.…”

“…This result was relevant; it demonstrated that all the components in the ν 3 profile evolved synchronously, which, in turn, signified that the species they originated from had comparable dynamics or, alternatively, that a single molecular species produced all the observed components. Albeit no conclusive evidence is yet available, we are inclined toward the second hypothesis, in view of previous studies on solvated low-molecular-weight compounds [ 73 , 74 ].…”

A Hyphenated Approach Combining Pressure-Decay and In Situ FT-NIR Spectroscopy to Monitor Penetrant Sorption and Concurrent Swelling in Polymers

“…The appropriateness of the theoretical model to simulate the 4954 cm –1 band shape is demonstrated in Figure , which also confirms that the proposed data analysis isolates correctly the signal of interest. The two-component structure is interpreted assuming the Gaussian part as being remnant of the gas-phase spectrum, while the sharp, Lorentz-like component is the purely vibrational transition active in the condensed phase (but not in the gas phase). , More specifically, the composite band shape is the consequence of the probe dynamics within the molecular environment, i.e., free rotation in the early stages of the relaxation process (0.2–1.0 ps), which produces the Gaussian component, and random rotational diffusion at later stages (the so-called Debye regime), giving rise to the Lorentz component. The well-developed Gaussian component is indicative of a sizeable free-rotation regime, which, in turn, suggests that the probe senses a poorly interactive or non-interactive environment.…”

Orientational Diffusion of Methyl Groups in Crystalline CH3F: An Infrared Study

“…In contrast, the E-type bands are broadened by both spinning and tumbling diffusion processes. For the orientational diffusion of various CH 3 X and CD 3 X molecules in liquids it has been shown that − where ζ is the first-order Coriolis coupling constant. For CH 3 F these constants for ν 4 , ν 5 , and ν 6 are equal to 0.089, −0.280, and 0.284, respectively …”

“…At temperatures higher than Δ H */ R ≈ 100 K the reorientations of CH 3 groups in solid CH 3 F must be expected to become quasi-free. Nearly free rotation has been reported for various CH 3 X molecules in the liquid phase and solutions. ,,,, Thus, it is of interest to compare the spinning diffusion constant for crystalline CH 3 F with that for the liquid phase of similar compounds. Extrapolating relation 10 to higher temperatures, we obtained the D ∥ value of 180(30) × 10 10 s -1 for the hypothetical “solid” CH 3 F at 295 K. This, as anticipated, agrees well with the D ∥ (295 K) values determined for liquid CH 3 Br, CH 3 I, and CH 3 CN, which also fall in the 180(30) × 10 10 s -1 region. ,, …”