14 January 1954

Dear Peter:

Mama and I stayed for a week in Washington with Edith and Sterling Hendricks, and then on Wednesday 6 January we flew home. Crellin had got home from Honolulu the day before, and he and George met us. We were sorry not to be able to go on to India -- and also to miss our week in Greece and our week in Israel. The Vice-President of the Hebrew University in Jerusalem wrote that he had arranged a fine schedule for us during the week, with a tour of north Israel -- Sea of Galilea, etc. -- which I had seen before, and also a tour of the Negev, the desert region to the south, going as far as (the northern region goes as far as Dan).

I am not sure that I told you just what our situation was. Our passport has not been revoked, nor was the validation for India refused. Instead, the Department of State simply delayed action, and when no action had been taken by the close of business on 31 December I withdrew the application, because even if the travel had been approved on 4 January, after the holiday, it would have been impossible for us to reach Hyderabad in time for the Congress, and the people at the Indian Embassy said that the Congress was the principal reason for inviting us. We are now hoping to make the trip a year from now.

Mama and I have decided to go to Honolulu for a two-weeks' trip. We shall arrive there at 6 P.M. on Tuesday 19 January, and stay for two weeks. Perhaps I shall give a lecture or two to the University or to the American Chemical Society while there. I am planning to take along the books by Charlotte Moore on term values of atoms -- these are publications of the Bureau of Standards, extending the tables of atomic energy levels in the book by Bacher and Goudsmit -- and to work over them, in order to obtain a set of approximate energy values for different electronic configurations of atoms, not including the interactions that give rise to Russell-Saunders states. That is, I want to know by how much the configuration 1s²2s²2p² lies below the configuration 1s²2s22p² for carbon, for example, and so on for the other atoms. The problem is complicated by the fact that the Russell-Saunders states often do not represent pure configurations, and accordingly some sort of averaging process has to be carried out. I am planning to look for a set of values of promotion energy that will show a reasonable dependence on atomic number. I am not trying for great accuracy. There are many chemical problems which require for their discussion the knowledge of these promotion energies, and so far as I know, nobody has published tables of them in recent years.

Then I am hoping to use the promotion energies, together with assumed bond energies and resonance energies, in the discussion of the electronic structure of the transition metals, in order to find out whether a simple treatment will indicate more or less clearly what the electronic configurations are upon which the metals are based. You remember that for copper, for example, the physicists have usually assumed the configuration 3d¹⁰4s, whereas I assume resonance between the configurations 3d⁸4s4p² and 3d⁷4s4p³.

Since getting home I have continued work upon the structure of collagen, and have found one structure that looks promising, except that it does not seem to give the right value of the density. The problem of the structure of collagen is a very difficult one. Crick sent me, last month, a copy of a letter that he has submitted to NATURE, describing a new structure that he has found. This structure involves two polypeptide chains twisted about each other. Each of the chains consists only of amide groups with the cis configuration. In each chain one amide group lies in a horizontal plane, and one in the vertical plane. The one in the vertical plane spands the pseudo identity distance 2.86 A. The group in the horizontal plane forms two hydrogen bonds with the corresponding group in the other chain, which is related to it by a horizontal two-fold axis. There is, however, serious steric hindrance between the hydrogen atom attached to the alpha-carbon atom ( groups) and a vertical amide group above or below does not show up in the electron micrographs.

Please write to us.

Love from

[Linus Pauling]