Dynamics and free energies of CH4 and CO2 in the molecular solid of the p-tert-butylcalix[4]arene
The dynamics of the guest molecules CO2 and CH4 in p-tert-butylalix[4]arene (TBC4) motion was studied from 100 K to 400 K using the velocity autocorrelation approach. The rattling motion of the CH4 guest molecules exhibit an increase in the Einstein frequency with increasing temperature as has been observed experimentally and in simulations for some rare gas clathrate systems. The CH4 molecule shows an increase from 75 cm-1 at 100 K to 91 cm-1 at 400 K. The CO2 rattling motion exhibits a single peak and less temperature dependence going from 76 cm-1 at 100 K to 72 cm-1 at 400 K. The rotational spectra for CO2 exhibit two peaks at 100 K with the higher frequency peak shifting to lower frequency with increasing temperature. The computed rotational Einstein frequencies go from 86 cm-1 at 100 K to 71 cm-1 at 400 K. The temperature dependent Gibbs absorption free energies of the guest molecules CO2 and CH4 in TBC4 have also been studied at 1 bar using thermodynamic integration from 10 K to 400 K. As expected, the simulated absorption free energy for CO2 is greater at all temperatures than for CH4. At 10 K, the simulated values of -11.4 kcal/mol and -8.4 kcal/mol for CO2 and CH4, respectively, while at 300 K the values are -5.4 kcal/mol and -4.4 kcal/mol. This work was performed at the Pacific Northwest National Laboratory (PNNL) and was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy (DOE). PNNL is operated by Battelle for the DOE.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 928265
- Report Number(s):
- PNNL-SA-58339; CHPLBC; AA2545050; TRN: US200815%%724
- Journal Information:
- Chemical Physics Letters, 453(4-6):123-128, Vol. 453, Issue 4-6; ISSN 0009-2614
- Country of Publication:
- United States
- Language:
- English
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