Interactions of diatomic molecules with graphite

Abstract

Amount of chemisorbed HzO, OH groups n d Figure 8. Relation between electrostatic field strength and surface H20 content on each of two kinds of surfaces: ( 0 ) (110) surface; (0) (100) + (101) surface.other hand, the F value of the (110) plane, F(,,,), remains constant at 1.54 X lo4 statvolt cm-l at evacuation temperatures from 25 to 150 OC. The F(llo, value then increases almost linearly with decreasing amount of surface hydroxyls, which also impliesthe (110) surface to be homogeneous. Strictly speaking, on the extremely dehydroxylated surfaces the F(',,) curve deviates slightly to higher values from the straight line, probably because af the presence of active sites or various kinds of surface defeds. In conclusion, the two kinds of surfaces, (110) and (100) + (101), are found to be homogeneous, respectively. Furthermore, it is interesting to see that the F(llo) value on the bare (110) surface is 3.26 X lo5 statvolt cm-', being remarkably larger than the average F value of the actual surface (Figure 4).In the bulk of the rutile crystal, the coordination numbers of Ti4+ and 02-are 6 and 3, respectively, so that the formal charges of Ti4+ and 02-are +2/3e and -2/3e per bond, respectively, where e is the electronic charge. On the other hand, in the bulk of the wurtzite crystal the coordination numbers of both Zn2+ and 02-are 4, so that the formal charges of Zn2+ are 02-is + 1 / 2 e and -1/2e per bond, respectively. Thus it can be expected that the F value of the bare (110) surface of rutile is larger than that of the bare (10x0) plane of ZnO. However, the experimental F values of rutile and ZnO are found to be almost equal, Le., 3.26 X lo5 and 3.38 X lo5 statvolt cm-l, respectively. Upon the analysis procedure of heat of adsorption stated above, it is assumed that the heat values of the organic adsorbates on the hydroxylated (110) surface are identical with those on the hydrated (100) + (101) surface, but in practice the former may be larger than the latter. With this point of view taken into account, the true F value of the (110) surface of rutile may be larger than the F(',,, value shown in Figure 8. Acknowledgment. I thank Professor Tohru Takenaka of Kyoto University for his kind advice and helpful suggestions and Professor Mahiko Nagao of Okayama University for much help in the heabof-immersion experiments. I also thank Professor Tetsuo Morimoto of Okayama University for his helpful discussions and constant encouragement throughout this work. RegistryLow-coverage isotherm data for the adsorption of 0 2 on exfoliated graphite are reported and analyzed by using the virial adsorption isotherm. The molecule-solid and the adsorbed molecule-molecule second virial coefficients are obtained for this system over a range of temperature. These data are compared with theory, and best-fit parameters for the site-site moleculesolid interaction potential are given. In addition, a comparative study of the molecule-molecule interactions for 02, N2, and CO is presented, based on the molecule-molecule virial coefficients rep...

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