Hoffman David J, Fayer Michael D
Department of Chemistry, Stanford University , Stanford, California 94305, United States.
J Phys Chem B. 2017 Nov 16;121(45):10417-10428. doi: 10.1021/acs.jpcb.7b08301. Epub 2017 Nov 1.
The dynamics of the molecular glass former ortho-terphenyl through the glass transition were observed with two-dimensional infrared vibrational spectroscopy measurements of spectral diffusion using the small probe molecule phenylselenocyanate. Although the slow diffusive motions were not visible on the experimental time scale, a picosecond-scale exponential relaxation was observed at temperatures from above to well below the glass transition temperature. The characteristic time scale has a smooth temperature dependence from the liquid into the glass phase, but the range of vibrational frequencies the probe samples displayed a discontinuity at the glass transition temperature. Complementary pump-probe experiments associate the observed motion with density fluctuations. The key features of the dynamics are reproduced with a simple corrugated well potential energy surface model. In addition, the temperature dependence of the homogeneous vibrational dephasing was found to have a T functional form, where T is the absolute temperature.
通过使用小探针分子苯基硒氰酸盐进行光谱扩散的二维红外振动光谱测量，观察了分子玻璃形成剂邻三联苯在玻璃化转变过程中的动力学。尽管在实验时间尺度上未观察到缓慢的扩散运动，但在高于和远低于玻璃化转变温度的温度下均观察到了皮秒级的指数弛豫。特征时间尺度从液相到玻璃相具有平滑的温度依赖性，但探针采样的振动频率范围在玻璃化转变温度处出现了不连续性。互补的泵浦 - 探测实验将观察到的运动与密度涨落联系起来。动力学的关键特征可以用一个简单的波纹阱势能面模型来重现。此外，发现均匀振动退相的温度依赖性具有(T)函数形式，其中(T)为绝对温度。
