The absorption spectrum of benzene at 2800–2200A has been analyzed. The vibrational structure of the system has been found to be in agreement with the selection rules for a forbidden transition (1A1g→1B2u). The transition becomes possible when vibrations of type Eg+ distort the molecule. Only carbon frequencies have been found to be effective. The interpreted data are collected in series on page 211. The analysis is corroborated by comparison with the absorption of solid benzene at —259°C, with the absorption spectrum of heavy benzene and with the fluorescence spectra of both benzenes.

No abstract

No abstract

b) The formation of K 38 from calcium In a previous paper 3 results obtained by one of us in a study of the radioactivities induced in calcium by deuteron bombardment were reported. It was noted that a weak activity was observed in the potassium fraction separated chemically from the irradiated metal. It was suggested that this might be due to contamination, though it was thought, in view of the fact that the half-period did not agree with that of any well-known contaminant, that it might be due to K 38 formed thus:Ca 40 +H 2 ->K 38 +He 4 ; K 38 -+A 38 +e+.Following the production of K 38 by bombarding chlorine with alpha-particles, a search was made for this isotope in irradiated calcium. It has a sufficiently short half-life to have been unobservable in the previous experiments on accountThe coupling between light and heavy particles assumed in the Fermi theory of jS-decay makes it possible for high energy protons in passing through matter to transfer a considerable fraction of their energy to electrons and neutrinos. If we suppose that this coupling is a maximum for relative energies of the light and heavy particles of the order hc/R, with R the range of nuclear forces, and is small for much higher relative energies, the most important process which occurs, for sufficiently energetic protons, can be pictured as a sort of photodisintegration of the proton by the contracted Coulomb field of a passing nucleus, the proton changing into a neutron and emitting a positron and a neutrino. With a coupling of the type described, and of of the time needed for the chemical separation adopted.Calcium metal was, therefore, bombarded with deuterons for half an hour and, following solution in HC1 and the addition of inactive KC1, potassium was precipitated by means of perchloric acid and ethyl alcohol. In consequence the precipitate was contaminated with radioactive scandium. 3 However, on correcting for this it was found that K 38 was present, the decay curve corresponding to a half-period of 7.6 ±0.2 minutes. This curve is reproduced in Fig. 5.The decay of this precipitate was measured until its corrected intensity was less than the natural leak of the electroscope, but no evidence was obtained of the 12.4 hour period of K 42 . The expected reaction Ca 44 +H 2 ->K 42 +He 4 ; K 42 ->Ca 42 +e~ would thus appear to be rather improbable. V. CONCLUSIONIn conclusion we wish to thank the staff of the Radiation Laboratory for their cooperation, and especially Professor E. O. Lawrence for his interest and encouragement. The investigation has been aided by grants to the laboratory from the Research Corporation, the Chemical Foundation and the Josiah Macy, Jr. Foundation. the magnitude required by the proton-neutron forces, processes involving more than one pair of light particles will be relatively rare. The cross section for the disintegration of a proton of energy E is found to be of the order 27r(h/Mc)RZW In 2 {E/Mc 2 ),and is very small, even for heavy nuclei. The mean energy given to the positron per disintegration is of the ord...

An attempt has been made to give a coherent interpretation of the absorption systems of benzene vapor in the far ultraviolet including the Rydberg series. The following assignments are proposed: A forbidden transition of symmetry 1A1g→1B1u is suggested for the bands at 2050 to 1850A and an allowed 1A1g→1E—u transition for the much more intense bands at 1850 to 1650A. The continuous background in the latter region may possibly be due to a transition involving a C–H dissociation. The observed two Rydberg series can both be assigned to allowed transitions of symmetry 1A1g→1E—u.