March 23, 1937
Dr. Maurice L. Huggins
Kodak Park Works
Eastman Kodak Company
Rochester, N. Y.
Dear Maury:
The arrival yesterday of a letter from Urey asking about your manuscript reminded me of it. It arrived here along with other mail during ay absence on a trip to Berkeley, and since my return I have been busy and have put off doing various things in an inexcusable manner.
I am glad to hear that your work is starting off well. I am sure that you could have plans of Brockway's electron diffraction apparatus if you want them, although perhaps it would be necessary to have some of them traced, at a small cost. Fred Henson did not build the outfit, which was made in our own astrophysics shops, which are now busy with astrophysics work and could not do outside work anyway. I doubt that there would be any advantage to having Hanson construct the apparatus for you. Moreover, I do not know whether the apparatus would be very satisfactory for work on surfaces and thin films; after seeing the beautiful photographs published by Finch and Quarrell, I think that you would do well to build an outfit like theirs.
In regard to your paper I have the following comments to make.
On page 4 you say that there must be more L L resonance in HF than ionic resonance. I doubt that this statement and the following statements based on it are correct; in any case, they need some support. The only calculations I know of which bear on the question are those of Weinbaum and Roson for H2; these show that the ionic contribution is as great as the contribution of a better function than an L orbital. In HF the ionic contribution would no doubt be still greater in relative importance. I might point out that there is a definitely incorrect statement on this page; an ionic state of a molecule cannot be considered as involving orbital.
I doubt, for these same reasons, that FL
KHL
LF structures are important for HF2- and that the other structures suggested for compounds of first row atoms are of much significance.
On page 7 you point out that 4 coplanar bonds around a cuprie kernel seem to disagree with my original theory. I did not understand at first that a single electron is not able to hold tenancy of an orbital which can be made useful in bond formation. This is seen to be true, however, inasmuch as an orbital used in bond formation contributes penetration energy of one electron, and there is accordingly no energy loss in transferring the orbital from occupancy by one unshared electron to use in bond formation. There is a loss in penetration energy when an unshared electron pair is promoted; that is, an unshared pair can reserve an orbital but a single unshared electron cannot.
In general, my feeling is that your idea about the use of higher orbitals such as 4d orbitals for the iron group is a good one, but that you are too extreme in rejecting ionic structures in favor of structures of this type in all cases. For example, it is hard to understand why the 4s4p
24d square bonds are not formed more often. You may be interested to learn that we have discovered a ferric complex with three unpaired electrons. We also have some evidence from magnetic work on disulfides regarding the use of 4d orbitals.
Finally, I would like to mention again the "Undergraduate Thesis, 1919" to which you refer twice in this paper. You remember that I inquired for this at the U. C. library and then of you, and finally after you wrote me that it was a term paper in Professor Bray's class, of him, without success. It seems that under these circumstances you should be careful about this reference, and perhaps should refer instead to published papers or existent manuscripts.
I am sending a copy of this letter to Urey, in answer to his request for my opinion.
With best regards, I am
Sincerely yours,
Linus Pauling
LP:mrl
March
23, 1937
