ENGINEERING RESEARCH INSTIT'ITE THE UNIVERSITY OF MICHIGAN ANN ARBOR Quarterly Report No. 7 INFRARED STUDIES OF CRYSTALS II 15 November 1955 to 15 February 1956 Go B. B. M. SUTHERLAND Principal Investigator Project 22355 SIGNAL CORPS. DEPARTMENT OF THE ARMY CONTRACT DA 36-059 sc-56756 SC PROJECT 152B, DA PROJECT' 3-99-15-022 SqUIER SIGNAL LABORATORY, FORT MONMOiJTH, N. J. March 1956

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN TABLE OF CONTENTS Page I. PURPOSE OF THE RESEARCH 1 II. ABSTRACT 1 III. PUBLICATIONS AND CONFERENCES 1 IV. FACTUAL DATA 2 V. CONCLUSIONS 4 VI. FUTURE PROGRAM 4 VII. PERSONNEL 4 ii

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN Quarterly Report Noo 7 INFRARED STUDIES OF CRYSTALS II I. PURPOSE OF THE RESEARCH The general purpose of this research is to complete the investigations started in May of 1951 under Contract DA 36-039 sc-56736 on the infrared spectra and structure of barium titanate, brucite, mica, gypsum and diamond. IIo ABSTRACT This report summarizes the progress which has been made during the past three months on the preparation of our previous results for publication. No new experimental work has been done. III. PUBLICATIONS AND CONFERENCES No publications have been made during the period covered by this report. A conference was held at Ann Arbor with Dr. Ho Kedesdy and Mro Ao Schwarz on Wednesday, January 31st at which the arrangements for the termination of this contract were discussed. It was agreed that during the remainder of the time preparation of the previous work for publication should be given top priority. Some of the current problems in infra-red reseat.^ at the Signal Corps Laboratory were discussed, especially the estimation of oxygen, in silicon. 1

L ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN IVo FACTUAL DATA A, BARIUM TITANATE AND MICAS Nothing new to report. B. BRUCITE The whole of the work on brucite and portlandite is being prepared for publication. The theory of the anomalous bands is being investigated by Dr. K. Hechto The following note is being submitted to the Journal of the Optical Society: Crystal Structure of Brucite and Portlandite in Relation to Infrared Absorption Ro T, Mara * and G, B. B, Mo Sutherland Physics Department University of Michigan Ann Arbor, Michigan The infra-red spectrum of brucite (Mg(OH)2) shows an unexpected band with a very interesting fine structure in the region between 2.53- and 3o55o When we first reported this phenomenon 1 the conclusion was drawn that the unit cell in brucite must be larger than that found from X-ray analysis 2 and that the positions of the hydrogen atoms had been incorrectly deduced.o This conclusion was questioned by Petch and Megaw 4 who reinvestigated the crystal structure of brucite and also that of the isomorphous crystal, portlandite (Ca(OH)2), finding no evidence in either case for a unit cell larger than that found in the earlier X-ray worko Petch and Megaw 4 also reported that the inf'ra-re~d ~pDtum of portlandite exhibited features very similar to those found in brucite. Since the crystals of portlandite used in these observations was much more nearly perfect than the brucite crystals, it was clear that the anomalous fine structures could not have arisen from the use of an imperfect crystal. * Present address, Physics Department, Gettysburg College Gettysburg, Pennsylvania 1 - 2

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN The basis for our conclusion that the unit cell in brucite must contain more than two hydroxyl ions was that the fine structure was shown to be due essentially to hydrogenic vibrations and since it seemed unlikely that much of it could be due to the combination of OH stretching with OH deformation modes 5, it was assumed that more than one OH stretching fundamental was being observed. Recently we have examined the infra-red spectrum of brucite at the temperature of liquid nitrogen and we find that all of the bands on the low frequency side of the center of the band disappear. This shows that these bands are combination difference frequencies arising from energy levels due an exceptionally low OH deformation mode and that it is possible to explain the spectrum (in principle at least) without invoking a larger unit cell or changing the equilibrium positions of the hydrogen atoms from those proposed originally by Bernal and Megawo3 The possibility that a low frequency "libration" of the OH ion might be responsible for the fine structure was also pointed out by Hexter who had observed an analogous effect in the spectrum of crystalline iodoform. Our observations at low temperature confirm Hexter's suggestion, although the full explanation of the fine structure still presents many difficulties. These will be discussed in a future and fuller presentation of this work. It should be added that the hydrogen atoms in portlandite have recently been located by Petch h using refined Xray analysis. Also Elleman and Williams 8 have located the protons in brucite by nuclear magnetic resonance. In each case the work confirms the Bernal-Megaw structure. We are grateful for financial support from the U. S. Army Signal Corps under Contract DA-36-039 sc-56736. 1R. T. Mara and GoB.B.M. Sutherland, J. Opt. Soc. Am. 43, 1100 (19553). 2Go Aminoff, Geol. Foreno 1 Stockholm Forho 41, 407 (1919). J. D. Bernal and H. D. Megaw, Proc. Roy. Soc. (London) A 151, 384 (19355). Ho Eo Petch and Ho D. Megaw, J. Opt. Soc. Amo 44, 744 (1954). Ro To Mara, PhoD. Dissertation, University of Michigan (1954). 5

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN - 6 R. M. Hexter and H. Cheung, Ohio State Symposium on Molecular Structure 1955 p.22. Also private communication from R. M Hexter 7 H, E. Petch, Phys. Rev. 99, 1635 (1955). 8 Private Communication from Professor Dudley Williams. C. DIAMOND Nothing especially new to report. D. GYPSUM The manuscript of the paper on gypsum is almost complete. It has taken much longer than was anticipated to get this material into shape. A copy of the manuscript will be included in the Final Report since there is not sufficient time for it to be reproduced in full (with diagrams) for this report. V. CONCLUSIONS Nothing new to report. VII. FUTURE PROGRAM Work will continue on the preparation of manuscripts for publication. VIIIo PERSONNEL The following people have been engaged on the work reported here: Professor GoB.B.M. Sutherland (part time) Dr. K. Hecht (part time) Mro A, Dockrill (part time on model construction and preparation of diagrams) Mrs. C. Walker (part time on typing and secretarial work). 4