A paper at a scientific session

Mr. Chairman, Dear Colleagues, Ladies and Gentlemen!

(1) It is a great pleasure for me to attend this session and to
have an opportunity to give a talk here.

(2) In my talk today I am going to deal with the phase transi­
tion 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 the 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 theoreti­
cal and practical interest.

(3) 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 fi­
nally I shall comment on the nature of the phase transformation
in solid furan.

(4) First then, the experiment. A low temperature infrared cell
has been built where the temperature is automatically controlled
throughout the range of 80-300 К with a very high precision,
namely 0.1 K. By condensation of furan vapor on a window
cooled at a temperature below 150 К 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
Perkin-Elemer model 125 spectrometer.

(5) Now I'll pass over to the consideration of the results ob­tained. Slide 1, please. The slide shows the results of one series of measurements in the 580-620 cm-1 region. The spectra are re­corded in steps of 0.1 К near the transition point during heating. 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 multiplet struc­ture of the exciton bands observed in the low temperature phase indicates an ordered crystal. In the high temperature phase the

(6) 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.

When the presentation of the paper is over the speaker usually takes questions. When answering, the speaker may feel the need to comment on the question or apologize for a certain looseness in definitions, citations, data estimation etc. Here are some possible ways of a) responding to questions and b) apologizing for lack of clarity in answers.

a) commenting on a question or a point of view expressed

That's a good question. Thank you for asking it.

It's a difficult/intricate question. I can't give a detailed answer