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Single-wall carbon nanotubes (SWNTs) prepared by the arc discharge method were oxidized using nitric acid. The samples were analyzed by using Raman scattering and Fourier transformed infrared spectroscopy (FTIR). The FTIR results indicate the presence of –COOH acid groups in the treated samples. The up shifts observed in the radial breathing mode frequencies suggest that SWNTs behave as donors after the acid treatment, with charge transfer occurring from the nanotubes to the –COOH groups. Ab initio calculations of SWNTs interacting with –COOH acid groups support the charge transfer process from the nanotubes to the carboxyl groups.