Studies on the proton dynamics and melting of ice crystals

在这项研究中，我们建立了一种新的荧光方法，可以用于研究冰晶中的质子动力学。选择2-萘酚分子作为荧光探针，用皮秒脉冲激光激发。结果表明：(1)用激发态质子转移(ESPT)模型很好地解释了脉冲激发后荧光的衰减曲线。(2)在120K附近观察到荧光寿命从5 ns到2 ns的递减，这与120K以上质子在冰中迁移率的增加是一致的。这都归因于L缺陷迁移率的增加。(3)在72K附近观察到了寿命缩短和快慢组分强度比的增加。这一温度被确认为质子有序化转变，这种转变只在介电和热学测量中观察到。结果表明，我们的荧光方法具有较高的…由于跃迁附近的涨落增大，使得探针分子的激发态不太稳定，寿命变短，因此探测探针分子附近质子有序化的局域趋势的灵敏度更高。我们的结论是，探针分子的加入将局部打破所谓的冰规则，并在没有KOH掺杂的情况下激发质子有序性前夕。(4)为了了解萘酚分子是如何包含在冰晶中的，我们采用真空升华法生长了纯的萘酚晶体。通过对掺萘酚冰晶光谱的比较，归属了荧光光谱中的振动结构。结果表明，随着包裹体类型的不同，冰的声子有一个特征的零声子漂移，这将有助于冰的熔化转变的继续研究。这些结果已部分发表在几种期刊上，并于1996年8月在新汉普郡举行的国际冰物理与化学会议上发表。(Proc.将很快在J.Phys.Chem上发表。)较少

In this study, we have established a new fluorescence method which can be used for the study of proton dynamics in ice crystals. 2-naphthol molecule was chosen ad the fluorescence probe to be excited by a pico-second pulse laser. The following results were obtained.(1) The decay curves of the fluorescence after the pulsed excitation were well explained by the ESPT (excited state proton transfer) model.(2) A stepwise decrease in the flurescence lifetime from 5ns to 2ns was observed near 120K,which is consistent with the increase in the mobility of the proton in ice above 120K.They were both attributable to the L-defect mobility increase.(3) The lifetime shortening as well as the increase of the intensity ratio between the fast and slow components were observed around 72K.This temperature is identified as the proton ordering transition, which have been observed only in KOH-dopedice in dielectric and calorimetric measurements. The precent result shows that our fluorescence mothod has high … More sensitivity to detect the local tendency of proton ordering near the probe naphthol moleculesince the fluctuation increase near the transition makes the excited state of the probe molecule less stable and makes the lifetime short. We conclude that the inclusion of the probe molecule would locally break the so-called ice rule and stimulate the proton ordering eve without KOH-doping.(4) In order to see how the naphthol molecule is included in ice crystal, we grew a pure naphthol crystal by a vacuum sublimation method. From the comparison of the naphthol-doped ice spectra, we have assigned the vibrational structure in the fluorescence spectra. The result shows that there is a characteristic zero phonon shift depending on the type of inclusion, which will be useful for the continuing study on the melting transition of ice.These results were partly published in several journals and also presented in the International Meeting on the Physics an Chemistry of Ice held in New Hampshire in Aug.1996. (Proc.will be soon published in J.Phys.Chem.) Less