December 2, 1968

Mr. and Mrs. Kenneth Hunter

Salmon Creek

Big Sur, Calif. 93920

Dear Kenneth and Joan:

I am planning to have a piano (our piano in Pasadena) brought up to the ranch, and put in the living room of our house. Dr. Gustav Albrecht is arranging about transportation.

Dr. Albrecht has lived at the ranch, and knows everything about it.

There is the possibility that the piano will be delivered at the ranch sometime during the week beginning Monday 16 December, or we may put it off until later.

I suggest that you telephone me at my office in the University of California in La Jolla about 11 o'clock in the morning of Monday 9 December. If I am not there you can try again the following day. The telephone is 71U-U53-2000, extension 2005. I am having you telephone to the office in the University, because I want the piano to be a surprise to Ava Helen.

I hope that everything is going along well with you. Please remember to telephone to us at our house in La Jolla every Sunday.

Sincerely,

Linus Pauling

December 2, 1968

Professor Peter J. Pauling

Chemistry Department

University College London

Gower Street WC 1

London, England

Dear Peter:

I have received another packet of Penguins, forwarded from Santa Barbara, with 60C extra postage due.

I trust that you have changed the address by this time. The postal regulations provide for forwarding mail only during a period of two years, and, moreover, it is expensive to have these packages forwarded.

I am still having trouble finishing the manuscript—that is, getting the exercises written. I have done the rest of the work. I think that Stan has had someone reading the manuscript, but I have not received comments as yet.

I wish that it had been possible for you to stay to help me for another month. I probably would have got everything finished, and done a better job, if you had been at hand.

Much love from,

Daddy

December 5, 1968

Mr. Stanley Schaefer

W. H. Freeman and Company

660 Market Street

San Francisco, Calif. 94104

Dear Stan:

Under separate cover I am returning the laboratory manual by [...].

I think that it would be worth publishing, and I would be willing to have it as a book in my series.

As you pointed out, the writing is terrible. The job of editing the manuscript would be a big one.

The subject matter looks very good to me. I have checked a good number of pages, and have found only one real error. It is on page 5 of the experiment on x-ray powder diffraction technique, about the middle of the manuscript. The figure showing the structure of carbon dioxide, at the bottom of the page, is wrong. The molecules are shown in only two different orientations, whereas in fact they have four different orientations.

Also, there is an error in judgment on the same page, involving the fluorite structure. The structure is shown much better by having a fluorine atom at the corner of the unit cube, rather than a calcium atom.

It is evident that the author is an able person, who understands what she is writing about.

Sincerely,

Linus Pauling

LP:jj

December 9, 1968

TO: Art Robinson and Ian Keaveny

FROM: Linus Pauling

SUBJECT: Structure of Fluorine

Here is an analysis of the problem of the structure of fluorine.

He assume that the molecule, with internuclear distance 1.44 Å, can be treated as two interpenetrating spheres, each with van der Waals radius 1.6 Å, and that van der Waals attraction will bring each atom into contact with as many atoms of neighboring molecules as possible.

We start with a hexagonal packing of molecules in the basal plane, with their axes perpendicular to this plane. By tipping all of the molecules in the same direction the atoms of the upper layer can be brought into contact with atoms in the lower layer, while retaining contact with the atoms in the same layer. A tilted hexagonal layer of molecules is thus obtained (rather, a layer of tilted molecules). There are two ways of tilting: either toward one of the nearest atoms, or at 30° from this direction, between the atoms. I think that calculation of the contact distances will show that the first is the better.

The amount of displacement of the top layer relative to the bottom is 0.5 Å, corresponding to a tilt of about 20.3o . The tilt is so small that it is convenient to refer to the double layer in the usual way for hexagonal layers, by use of the letters A, B, and C.

The tilt can be expected to lead to a decreased symmetry of the double layer, so that axes B and A will no longer be in the ratio 1.732. I think that a prediction of the amount of change in axial ratio could be made by allowing this ratio to change, as well as the tilt, and making a least-squares treatment of the van der Waals contact distances. A change 3 percent, as in alpha fluorine, is not unreasonable.

The structure of the crystal would result from packing these double layers over one another, so that the bottom atoms of the upper double layer fit into the triangular positions of the top atoms of the lower double layer. If the lower layer is described by A, the upper layer can be described by B; the same structure would be obtained by putting the upper layer in C.

The deformed layers can be fitted together only if the tilt for the second layer is in the same direction as for the first layer, or in the opposite direction. Tilts at 30° or 60° to the rectangular axes of a layer would not occur, unless the interaction energy between layers were great enough to deform the layers in the way required to achieve the fit.

If the second layer is tilted in the same direction as the first layer, the third in the same direction as the second, and so on, a monoclinic structure is achieved with the B axis 5.5 Å long. This unit of structure does not agree with that observed for fluorine or that observed for alpha-oxygen.

If the second layer is tipped in the opposite direction (along the 3.28 Å axis) from the first layer, the third opposite to the second, and so on there are two possible structures. If the sequence of layers is ABAB...an orthorhombic structure is obtained. If the sequence of layers is ABCABC.a monoclinic structure is obtained, with monoclinic angle about 103°, A = 3.28, B = 5.50, and C = 7.34 Å. This structure seems to be the probable one for alpha fluorine.

The coordinates are predicted to have the values x = 0.190, y = 0.049, z = 0.095, relative to an origin at the center of a fluorine molecule. I think that the parameter values need to be changed to agree with the choice of origin in the International Tables, probably by adding 0.250 to two of the parameters (I do not have the Tables at hand).

I think that we could carry out an argument involving isotropy of polarizability to make it reasonable that layers with alternating positive and negative tips would interact more strongly than layers tipped in the same direction. I do not see any simple way to account for the greater stability of the monoclinic structure of this sort than of the orthorhombic one.

The unit cell of oxygen does not correspond to the foregoing argument. Instead, it involves a tip in the direction at 90° or 30° from that described above for fluorine. A tip of this sort leads to long strings (along the B axis) of oxygen molecules in parallel rectangular orientation. I think that the magnetic interactions of the triplet molecules might well be responsible for the assumption of this structure, which is, I judge, antiferromagnetic, probably with antiparallel spins alternating along these rectangular rods. The ratio A/B differs from 1.732 by 10 percent, three times as much as for fluorine. Near the end of their fluorine paper the authors say that a tilt of about 3° is consistent with the data that they give (Barret, Meyer, and Wasserman) in J. Cham. Phys. 47, 592 (1967). I think that a larger tilt would be expected for this sort of tilting than for fluorine, perhaps 16°, and it might be worth while to look at this oxygen paper, to see how good the reported intensities seem to be. Perhaps we should check up on the rhombohedral oxygen phase and the high-temperature phases of both oxygen and fluorine.

Linus Pauling

LP:jj

December 9, 1968

Dr. Martin M. Katz

Chief, Clinical Research Branch

National Institute of Mental Health

5454 Wisconsin Avenue

Chevy Chase, Md. 20203

Dear Dr. Katz:

I am grateful to you for your letter of 2 December and the copy of your article on ascorbic acid level in relation to psychological test behavior.

Our work is going along satisfactorily. We are giving doses of vitamins by mouth and analyzing samples of urine. Much of our work so far has been on the development of more rapid and reliable methods of analysis. We are making use especially of gas chromotography, at the present time.

Sincerely yours,

Linus Pauling

LP:jj