Phase Transitions of Amorphous Solid Acetone in Confined Geometry Investigated by Reflection Absorption Infrared Spectroscopy

Abstract

We investigated the phase transformations of amorphous solid acetone under confined geometry by preparing acetone films trapped in amorphous solid water (ASW) or CCl4. Reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD) were used to monitor the phase changes of the acetone sample with increasing temperature. An acetone film trapped in ASW shows an abrupt change in the RAIRS features of the acetone vibrational bands during heating from 80 to 100 K, which indicates the transformation of amorphous solid acetone to a molecularly aligned crystalline phase. Further heating of the sample to 140 K produces an isotropic solid phase, and eventually a fluid phase near 157 K, at which the acetone sample is probably trapped in a pressurized, superheated condition inside the ASW matrix. Inside a CCl4 matrix, amorphous solid acetone crystallizes into a different, isotropic structure at ca. 90 K. We propose that the molecularly aligned crystalline phase formed in ASW is created by heterogeneous nucleation at the acetone-water interface, with resultant crystal growth, whereas the isotropic crystalline phase in CCl4 is formed by homogeneous crystal growth starting from the bulk region of the acetone sample.

Formation of Cubic Ice via Clathrate Hydrate, Prepared in Ultrahigh Vacuum under Cryogenic Conditions

“…Isothermal time-dependent RAIR spectra of 150 MLs of pure acetone (Figure S1), measured at different temperatures (115, 120, and 125 K), showed a major feature at ∼1718 cm −1 due to bulk acetone. 49,55,56 This confirmed that the 1721 cm −1 peak is entirely a new feature and arises only because of acetone hydrate and not because of bulk acetone or its aggregates. Temperature-dependent RAIR spectra shown in Figure S2 suggest that acetone hydrate starts to form at 130 K. However, it is not stable in this condition and dissociated within 3 h. The inset of Figure 1 shows the reduction of C=O stretching band with time and resulted in a weak feature at ∼1702 cm −1 .…”

“…Taking the area under the 1721 cm –1 peak, the amount of acetone in the hydrate form was estimated to be 32.59% of the total acetone. Isothermal time-dependent RAIR spectra of 150 MLs of pure acetone (Figure S1), measured at different temperatures (115, 120, and 125 K), showed a major feature at ∼1718 cm –1 due to bulk acetone. ,, This confirmed that the 1721 cm –1 peak is entirely a new feature and arises only because of acetone hydrate and not because of bulk acetone or its aggregates. Temperature-dependent RAIR spectra shown in Figure S2 suggest that acetone hydrate starts to form at 130 K.…”

“…At 135 K, the O−H bending band became featureless, and therefore, it was neglected in the spectra. The C=O stretching band at 0 h shows two features at ∼1721 and ∼1709 cm −1 , which are attributed to acetone hydrate 52−54 and ASW-trapped acetone, 55 respectively, based on previous IR studies. These two features were deconvoluted to predict the actual amount of acetone in the hydrate form with respect to the total acetone present.…”

Effect of Electric Field on Condensed-Phase Molecular Systems. I. Dipolar Polarization of Amorphous Solid Acetone

“…The Journal of Physical Chemistry C Article 1709 cm −1 rather than at 1708 cm −1 as assigned in the previous work, 27 to achieve a better fit. However, this amount of difference is not physically meaningful.…”

Tailoring Electric Field Standing Waves in Reflection–Absorption Infrared Spectroscopy to Enhance Absorbance in Buried Molecular Layers

“…Highly sensitive and selective techniques are required to probe buried layers and interfaces that can be found in the natural environment − as well as in manufactured systems, − where specific reaction mechanisms and transport processes occur that are still only partially understood. For instance, electrochemical and catalytic reactions, − transport within the lipid bilayer of the cell, ,,, and partition of solutes in multiphase fluids ,, can be understood by scrutinizing precisely interfaces and buried molecular layers where these phenomena take place. , Conventional in situ and non-invasive methods such as sum frequency generation (SFG), ,,,− Fourier transform infrared (FTIR) spectroscopy, ,− ,,− grazing incidence X-ray diffraction (GIXD), − and Raman spectroscopy , have been applied to improve our understanding of these processes. , Despite the high selectivity of SFG and GIXD for interfaces, they lack the capacity to investigate the bulk of buried molecular layers. As for the usual methodologies and techniques relying on FTIR and Raman spectroscopy, they are commonly found to have a poor surface sensitivity or to be unselective to the depth profile of multilayer systems.…”