Pentacene deposited on silica adopts two different packing arrangements. The kinetically favorable thin-film phase (TFP) occurs at lower substrate temperatures and thinner deposition thicknesses relative to the thermodynamically stable bulk phase (BP). Both phases orient in a tilted edge-on motif, where the BP is tilted further from the perpendicular, identifiable using X-ray diffraction (XRD) techniques. Different types of growth on SiO 2 have been proposed. One is that deposition at the interface begins with the TFP, independent of substrate temperature, while the BP deposits over it after a temperature-dependent critical deposition thickness is reached. Others have found both phases to begin their temperaturedependent growth at the interface. Using an interfacial spectroscopic technique, vibrational sum frequency generation, paired with Fourier transform infrared spectroscopy and XRD, we determine that conucleation of both phases at the interface takes place during pentacene thin-film growth.

Fourier transform infrared, pump−probe polarization anisotropy, and twodimensional infrared spectroscopies were used to study the steady-state and time-dependent behavior of carbon dioxide dissolved in three different polymer systems. Gas reorientation dynamics in poly(methyl methacrylate), poly(methyl acrylate), and poly(dimethylsiloxane) were sensitive to the nature of chemical interactions between the gas and polymer, as well as whether the polymer was in a glassy or rubbery phase. The homogeneous dynamics experienced by the asymmetric stretching vibration were found to be fastest for rubbery polymers with weak, nonspecific gas−polymer interactions. Spectral diffusion was absent for the carbon dioxide vibrational mode in glassy poly(methyl methacrylate) but was activated for the chemically similar but rubbery poly(methyl acrylate). The vibrational dynamics are shown to have a direct correlation with the diffusivity of carbon dioxide through the polymer matrices.

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