The effect of classical and quantum dynamics on vibrational frequency shifts of H2 in clathrate hydrates.
نویسندگان
چکیده
Vibrational frequency shifts of H2 in clathrate hydrates are important to understand the properties and elucidate details of the clathrate structure. Experimental spectra of H2 in clathrate hydrates have been measured for different clathrate compositions, temperatures, and pressures. In order to establish reliable relationships between the clathrate structure, dynamics, and observed frequencies, calculations of vibrational frequency shifts in different clathrate environments are required. In this study, a combination of classical molecular dynamics simulations, electronic structure calculations, and quantum dynamical simulation is used to calculate relative vibrational frequencies of H2 in clathrate hydrates. This approach allows us to assess dynamical effects and simulate the change of vibrational frequencies with temperature and pressure. The frequency distributions of the H2 vibrations in the different clathrate cage types agree favorably with experiment. Also, the simulations demonstrate that H2 in the 5(12) cage is more sensitive to the details of the environment and to quantum dynamical effects, in particular when the cage is doubly occupied. We show that for the 5(12) cage quantum effects lead to frequency increases and double occupation is unlikely. This is different for the 5(12)6(4) cages for which higher occupation numbers than one H2 per cage are likely.
منابع مشابه
A molecular dynamics study of guest-host hydrogen bonding in alcohol clathrate hydrates.
Clathrate hydrates are typically stabilized by suitably sized hydrophobic guest molecules. However, it has been experimentally reported that isomers of amyl-alcohol C5H11OH can be enclosed into the 5(12)6(4) cages in structure II (sII) clathrate hydrates, even though the effective radii of the molecules are larger than the van der Waals radii of the cages. To reveal the mechanism of the anomalo...
متن کاملRaman spectroscopic studies of hydrogen clathrate hydrates.
Raman spectroscopic measurements of simple hydrogen and tetrahydrofuran+hydrogen sII clathrate hydrates have been performed. Both the roton and vibron bands illuminate interesting quantum dynamics of enclathrated H(2) molecules. The complex vibron region of the Raman spectrum has been interpreted by observing the change in population of these bands with temperature, measuring the absolute H(2) ...
متن کاملMolecular Hydrogen Storage in Novel Binary Clathrate Hydrates at Near-Ambient Temperatures and Pressures, excerpt from DOE Hydrogen Program 2006 Progress Report
Program Scope Clathrate hydrates are inclusion compounds in which guest molecules occupy the cages formed by a hydrogen-bonded water network [1]. Solid gas clathrate hydrates generally form at high pressures and temperatures near or even above the ice point. Pure hydrogen hydrates have been reported to form cubic structure II hydrates under extreme conditions (200 MPa at 280 K) [2]. We have rec...
متن کاملComputations of diffusivities in ice and CO2 clathrate hydrates via molecular dynamics and Monte Carlo simulations
We report molecular simulation studies of the diffusion processes in ice and CO2 clathrate hydrates performed using classical potential models of water ~SPC/E! and carbon dioxide ~EPM2!. The diffusivity of H2O in ice is calculated to be 1.3310 218 m s at 200 K using molecular dynamics simulations, a result in good agreement with experimental data. We also computed the diffusivity of H2O and CO2...
متن کاملThe Vibrational Stark Shifts of Sulfate Internal Modes in SO4 2– Doped Potassium, Rubidium and Cesium Selenates. A Quantum Model for Measurement of Crystalline Fields
A quantum theoretical basis for the experimentally observed vibrational Stark shifts of the sulfate internal modes in SO4 doped K2SeO4, Rb2SeO4 and Cs2SeO4 is presented. Analytical first order perturbation theoretical expressions are derived for the field-dependent wavenumbers of the 1 0 and 2 0 transitions, harmonic wavenumbers, as well as for the Stark tuning rate and the electrostatic field ...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید
ثبت ناماگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید
ورودعنوان ژورنال:
- The Journal of chemical physics
دوره 140 2 شماره
صفحات -
تاریخ انتشار 2014