It is a great pleasure for me to attend this session and to have an opportunity to give a talk here.
In my talk today I am going to deal with the phase transition of solid furan at 150.0 K. The polymorphic solids of furan have been investigated by calorimetric, X-ray, nuclear magnetic resonance, and infrared spectroscopic methods. However, all these experiments have not determined properties of solid furan in the vicinity of the phase transition at 150.0 K. Since vibrational excitations are very sensitive to the immediate environment of a given molecule in the crystal, we expected that their study should contribute to a better understanding of polymorphism in solid furan. The subject therefore, I believe, might be both of theoretical and practical interest.
In this talk I shall first present an experimental study of the infrared spectra of solid furan close to the phase transition. I shall then turn to the discussion of the results obtained. And finally I shall comment on the natural of the phase transformation in solid furan.
First then, the experiment. A low temperature infrared cell has been built where the temperature is automatically controlled throughout the range of 80-300 K with very high precision, namely 0.1 K. By consideration of furan vapor on a window cooled at a temperature below 150 K we obtained phase II. By heating the window we attained a total sublimation of the crystal at the transition temperature. The spectra were recorded on a Pertkin-Elemer 125 spectrometer.
Now Ill pass over to the consideration of the results obtained. Slide 1, please. The slide shows the results of one series of measurements in the 500-620 cm-1 region. The spectra are recorded in steps of 0.1 K near the transition point during eating. It should be stressed that in the high temperature phase the components of the band due to exciton splitting disappear. The infrared data suggest that the transition is sudden. The multiple structure of the exciton bands observed in the low temperature phase indicates an ordered crystal. In the high temperature phase the symmetry of transition is broken due to a reorientation disorder, so exciton structures of bands disappear in phase 1. Our infrared study of the out of plane mode in phase 1 shows that vibrational resonant takes about 0.04 sec. In other words, vibrational excitons in disordered crystals are localized excitons which map out the local structure of the solid. Slide 2, please.
From our data it can be concluded that the vibrational excitons interactions are very sensitive to the phase transition in solid furan and vibrational excitons are present in their disordered phase. Thank you.
Notes to the text:
solid furan - -
in the vicinity of - , - ,
vapor - 𠠠 -
exciton - -
band - -
2.Study various ways of:
A) stating the problem and its importance
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