ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN ARBOR TENTH QUARTERLY REPORT ON INFRARED STUDIES OF CRYSTALS 16 November 1953 to 15 February 1954 By G. B. B. M. SUTHERLAND Principal Investigator C. Y. PAN LIANG Project 1957 SIGNAL CORPS, DEPARTMENT OF THE ARMY CONTRACT DA 36-039 sc-5581 SC PROJECT 152B-0, DA PROJECT 3-99-15-022 SQUIER SIGNAL LABORATORY, FORT MONMOUTH, N. J. March, 1954

TABLE OF CONTENTS Page I. INTRODUCTION 1 II. ACCOUNT OF WORK DONE 2 III. FUTURE PROGRAM 4 ii

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN TENTH QUARTERLY REPORT INFRARED STUDIES OF CRYSTALS I. INTRODUCTION Purpose of the Research This has been outlined previously (cf. Report of June, 1953) and does not need to be repeated here. The main emphasis has continued on the determination of the positions of the hydrogen atoms in mica and brucite. Work has also been started on gypsum (Ca SO4 2H20) i.e., a crystal containing water of crystallisation. Personnel The following have been engaged on the work reported here: Professor G.B,.BM Sutherland, Director (Part time) Mrs. C. Y. Pan Liang (Half time) Mr. A. Dockrill (Part time) Mr. G. Allen (Part time) Mr. M. Hass (Part time, voluntary)

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN - II. ACCOUNT OF WORK DONE A. Mica Problem The principal effort has been directed to the elucidation of the biotite spectrum near 3p in terms of the coupled vibrations of eight OH groups in the unit cell. The earlier treatment (mentioned in the last report) was oversimplified. The new treatment may be summarised briefly by saying that the eight OH stretching vibrations couple to give eight modes of vibration bf the unit cell. There are two centres of symmetry in the unit cell, one of which belongs to four of the oxygen atoms and the other to the other four. There is a C2 axes parallel to the b axes of the crystals It is assumed that there is negligible interaction between OH groups separated by a layer of K ions. This means that the four active frequencies will reduce to two pairs of frequencies identical in numerical value. The first pair are associated with the band at 2.835t, since there should be no component along the c axis. The second pair are associated with the 2.735 band, since the major change of electric moment is now along the c axis, (cf. Ninth Quarterly Report). The quantitative agreement with the observed spectra is now very good, apart from a small anomaly connected with the 2.735 band. This last point is being checked experimentally and will also be reinvestigated theoretically. From the data it is now possible to determine the orientation of the OH groups in the unit cell with considerable accuracy, and this is being done. The full details (experimental and theoretical) will form the subject of a separate technical report. B. Brucite Since our previous results indicated that the unit cell in Brucite was larger than that found by X-ray work, one of our crystals (which were greatly superior to those on which the early X-ray work had been done) was sent to Dr. Megaw in Cambridge, England, She has made a fresh investigation but arrived at the same structure as before, i.e., two Mg (OH)2 ionic groups per unit cello We are therefore making another attempt to see whether the complexities of the OH absorption in Brucite can possibly be accounted for in terms of the original X-ray unit cello A detailed treatment by group theory is now in progress, 2

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN - Co Gypsum The absorption spectrum of thin plates of gypsum has been obtained between 2p and 20p/, using polarised radiation and various angles of inclination. Some of the bands are too intense for absorption work so the reflection spectrum is being obtained in these regions. It is possible to deduce the absorption spectrum from the reflection spectrum. The gross features of these spectra can largely be accounted for in terms of assignments made by previous workers on the Raman spectrum of gypsum. However, all the bands show some fine structure and interesting dichroic effects. A good deal more experimental work has to be done using different: aspects of the crystal before any detailed interpretation can be attempted, 3

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN III. FUTURE PROGRAM Work will continue on the theoretical interpretation of the spectra of mica and brucite. The experimental work will be concentrated on completing the data on gypsum, especially the reflection spectrum. 4