Fig shows the Raman spectra of

Fig. 8 shows the Raman spectra of CO2 (20%) + N2 (80%) hydrate, TBAC (3.3 mol%) semiclathrate, CO2 (20%) + N2 (80%) + TBAC (3.3 mol%) semiclathrate, TBAC (1.0 mol%) semiclathrate, and CO2 (20%) + N2 (80%) + TBAC (1.0 mol%) semiclathrate. The CO2 (20%) + N2 (80%) gas hydrate is known to form sI hydrate [9] and exhibits two peaks for enclathrated CO2 LY 450139 at 1276 and 1380 cm−1 and one peak for enclathrated N2 molecules at 2324 cm−1[9], [49], [50] and [51]. CO2 molecules captured in TBAC semiclathrate lattices were observed at 1273 cm−1 and 1380 cm−1 and N2 molecules at 2324 cm−1. A wavenumber shift (1276 cm−1 → 1273 cm−1) for CO2 molecules can be attributed to a slight difference in the size and environment of small 512 cages, where CO2 molecules are expected to be captured, in both sI gas hydrate and TBAC semiclathrates, even though the small 512 cages are common for both cases. N2 gas molecules enclathrated in both gas hydrate and semiclathrates, exhibit only one peak at 2324 cm−1 because N2 molecules are so small that the symmetric N–N vibration of N2 molecules captured in small and large cages of gas hydrates are not distinguishable [49] and [51]. Even though Raman spectroscopy cannot provide detailed information on CO2 distribution in the cages of gas hydrates or semiclathrates due to the impossibility of peak splittings for CO2 molecules enclathrated in different cages [36] and [52], Fig. 8 clearly demonstrates that both CO2 and N2 molecules are captured in the lattices of TBAC semiclathrates and that there is no structural transition due to the enclathration of guest gases in the lattices of TBAC semiclathrates.