The results of extinction measurements on submicron amorphous carbon particles performed between 1000 A and 8000 A are presented. The observations show the presence of a main peak which depends upon particle size and which tends to shift to shorter wavelengths for smaller dimensions, from 2430 A to 2350 A and beyond. Two other features, i.e. a shoulder at about 1800 A and a second peak at around 1500 A are also observed while the spectrum decreases as gamma exp -1.4 beyond 3000 A. The main band is interpreted as due to the surface plasmon mode of the ground electronic state at the surface of the grain; the other two features are interpreted as due to surface states located on the lower energy tail of higher energy excited electronic states. A comparison with previous experimental observations for similar material is also given. The absence of extra resonances in the interstellar extinction curves tends to suggest that the extinction is mainly due to grains located in dense clouds rather than to grains dispersed along the line of sight.
Extinction Spectra of Amorphous Carbon Submicron Grains in the UV - visible range
CAPOZZI, VITO GIACOMO;
1986-01-01
Abstract
The results of extinction measurements on submicron amorphous carbon particles performed between 1000 A and 8000 A are presented. The observations show the presence of a main peak which depends upon particle size and which tends to shift to shorter wavelengths for smaller dimensions, from 2430 A to 2350 A and beyond. Two other features, i.e. a shoulder at about 1800 A and a second peak at around 1500 A are also observed while the spectrum decreases as gamma exp -1.4 beyond 3000 A. The main band is interpreted as due to the surface plasmon mode of the ground electronic state at the surface of the grain; the other two features are interpreted as due to surface states located on the lower energy tail of higher energy excited electronic states. A comparison with previous experimental observations for similar material is also given. The absence of extra resonances in the interstellar extinction curves tends to suggest that the extinction is mainly due to grains located in dense clouds rather than to grains dispersed along the line of sight.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
