226 TABLE 85—Continued Taye. | length: § E,eV jog, Mb™| | | é6en , Mb | : FIL | op, Ib gan, Mb |" wom : 1219.0 1221.2 1223.5 1228 3 1230.0 | | 10.17 10.15 10.13 10.09 10.08 | | 3S. 32 146.06 AQF 46.35 40.12 | | 5 0) \ 0.23 | 1.71 ! O.BT 0.38 0.12 | 6 4 7 s 7 |; | | | 1 of.23 73.58 62.50 61.59 37.388 | 1 0.65 1.81 U.37 0.55 O37 i6 | h | 7 , 7 | 8 0.002 0.002 0). 002 0.001 0.002 | | 0.000 0.001 0.001 0.001 0.001 ” | ~Mb 0.09 0.25 0.08 0.05 0.08 ein, Mb | | | | | 0.02 0.05 0.04 0.04 0.02 fo |) Mb = 1073 em?. (b) Pressure =Q.1] torr. REFERENCES 1. Person, J. C. and Nicole, P. P. J. Chem. Phys. 49 5421 (1968). 2. Person, J. C. and Nicole, P. P. Argonne National Laboratory, Radiological Physics Division Annual Report, July 1967 through June 1968. ANL-7489, p. 108. 3. Person, J. C. Collision-Induced Ionization of Highly Excited Rydberg Levels of Polyatomic Molecules. Vith International Conference on the Physies of Electronic and Atomic Collisions. Cambridge, Massachusetts, July 28August 2, 1969. Book of Abstracts. p. 990. ISOTOPE EFFECTS IN THE PHOTOIONIZATION YIELDS AND THE ABSORPTION CROSS SECTIONS FOR ETHYLENE AND n-BUTANE* J.C. Person and P. P. Nicole The absorption cross section, ¢, and the photoionization yield, y (the probability that photon absorption produces ionization), are reported for CyH, and C.D, at 44 photon cnergics between 10.44 and 11.78 eV, und they are reported for »-butane and n-butane-dip at 37 photon energies between 10.56 and 1178 eV. For * Abstract of paper published in J. Chem. Phys. 49, 5421 (1968). ethylene, the nature of the isotope effeets on 4, ¢, and the photoionization cross sections, o:(0; no), imnelicates that the inerease in 7 upon deuteration is not the result of a simple competition between pretonization processes and atomie rearrangement processes in the superexcited states. The isotopeeffects for n-butane and the implications of the results for radiation chemistry are also discussed. A METHOD FOR ESTIMATING THE RELATIVE IMPORTANCE OF THE PLATZMAN COMPETITIVE IONIZATION PROCESS FROM ISOTOPE EFFECTS IN MOLECULAR PHOTOIONIZATION J.C. Person A graphical method is presented for estimating the minimum contribution to the total ionization of the Plataman competitive ionization process from data on the ionization vield. ». for deuterated (yp) and protonated (a1) molecules. The method assumes that one mayuse the simple kinetic model proposed by Platzman in which the ionization occurs either by direct ioniza+ tion or by the preionization of superexcited states in competition with atomic rearrangement processes leading to neutral products. It is also assumed that deuteration does not change the part of the ionization vield that results from direct jonization. The results are given in a figure which shows the curves (for the different values of mx) giving the maximum fraction of the ionization due to direct ionization as functions of a variable determined by the ratio of the observed yn/nu ratio to the maximum possible yn/na ratio. Another figure plots the maximum np/yu ratio for each value of qx - This paper presents a graphical method of analyzing data on the changes in ionization resulting from deuteration. The purpose is to estimate a lowerlimit of the contribution to the total ionization from the preioniza- tion of superexcited states that are in competition with atomic rearrangement processes leading to neutral products (e.g., dissociation). The methodis based on the simple kinetic model proposed by Platzman.“—In this model the ionization yield, 7() (the probability that