Department of Physics, Stockholm University
Monday 11 April
10:00 - 12:00
This licentiate thesis presents infrared spectroscopy studies on amorphous ices. Amorphous ices are solid states of water lacking long-range order. However, oxygen atoms still remain local tetrahedral structure by forming intermolecular hydrogen bonds. High-density amorphous ice (HDA) and low-density amorphous ice (LDA) are found to be glassy states of two distinct liquid states of water in molecular dynamics simulations. Furthermore, the transition of HDA to LDA is believed to undergo a liquid-liquid transition, from a high- (HDL) to a low-density liquid (LDL).
In this work, HDA is prepared in a mechanical press using a piston-cylinder setup in liquid nitrogen environment. LDA, or amorphous solid water (ASW) is formed by vapor deposition of water onto a cold substrate. We measure Fourier-transform infrared spectroscopy of both types of samples while heating at ambient pressure.
We report the first infrared spectra of high-pressure annealed HDA as well as of LDA obtained from the heating of HDA. We observe a shift toward higher frequencies for HDA, corresponding to the presence of broken hydrogen bonds. The full width at half maximum (FWHM) of the HDA spectrum is twice as much than LDA, indicating that HDA is more disordered than LDA. An intermediate state at 120 K is compared with a linear combination of HDA and LDA spectra. The fact that the intermediate state can be fitted by a linear combination of HDA and LDA, reveals a phase coexistence on the pathway of the transition. This is consistent with the first order-like phase transition reported in the literature.
Additional infrared spectroscopy on the formation and annealing of ASW is reported. We observe pore formation during vapor deposition and pore collapse while heating the sample. The spectra of porous ASW are shifted toward higher frequencies in respect to annealed ASW. The spectrum of the latter is found to be identical to LDA obtained from heating HDA.”