El Segundo, California). Graphite samples which have been heated resistively or by a laser to produce chaoite have been studied by an Ion Microprobe Mass Analyzer (IMMA). The yield of secondary negative ions from the starting material is typically C,-, C2-, and with lesser amounts of C3-and C*-but chaoite-containing areas produces ions of C,-to C,,-. IMMA spectra of allotropic forms of carbon will be presented. 163. Time dependence of carbon species distribution during the sublimation of graphite F. M. Wachi (Aerospace Corporation, El Segundo, California). Relative ion intensity measurements of C,+ and C,-species have indicated that the relative abundances of carbon vapor species change with time. This change in carbon species distribution appears to result from carbon evaporation from chaoite and possibly other carbon polymorphs that are different from graphite. 164. Laser effects on graphites at moderate argon pressures J. E. Colwell, J. D. McClelland, J. H. Richardson and E. H. Zehms (Aerospuce Corporation, El Segun~, CaliJbmia). Specimens of ATJ, CEP, and pyrolytic graphite at two orientations (c-axis parallel and normal to the laser beam) were exposed to a pulsed laser beam in argon at pressures from one to 100 atm. Incident energy at the specimen face was cu. 600 Ji cm. Examination of the crater and surrounding area by scanning electron microscopy reveals condensation or melting effects which are signifi~ntly affected by pressure as weli as by type and orientation of graphite.