represent the first Van Hove transition of metallic species (E11, metal), while the peak intensities representing the second (E22, semiconducting) and first (E11, semiconducting) Van Hove transition of the semiconducting species show little or no change. A relative decrease in metallic SWNT absorption features over semiconducting features represents a highly preferential functionalization of the metallic nanotubes. Raman spectroscopy Raman spectroscopy is a powerful technique with wide-ranging applications in carbon nanotube studies. Some important Raman features are radial breathing mode (RBM), tangential mode (G-band), and disorder-related mode. RBM features correspond to the coherent vibration of the C atoms in the radial direction of the nanotube. These features are unique in carbon nanotubes and occur with the frequencies ωRBM between 120 and 350 cm−1 for SWNT in the diameter range (0.7 nm-2 nm). They can be used to probe the SWNT diameter, electronic structure through their frequency and intensity (IRBM) respectively and hence perform an (n,m) assignment to their peaks. The addition of the moiety to the sidewall of the nanotube disrupts the oscillator strength that gives rise to RBM feature and hence causes decay of these features. These features are distinct for species of a particular nanotube (n,m) and hence enables to probe which SWNTs are functionalized and to what extent. Two main components of the tangential mode include G+ at 1590 cm−1 and G− at 1570 cm−1. G+ feature is associated with carbon atom vibrations along the nanotube axis. The G− feature is associated with vibrations of carbon atoms along the circumferential direction. The G-band frequency can be used (1) to distinguish between metallic and semiconducting SWNTs, and (2) to probe charge transfer arising from doping a SWNT. Frequency of G+ is sensitive to charge transfer. It upshifts for acceptors and downshifts for donors. Lineshape of G− is highly sensitive to whether SWNT is metallic (Breit-Wigner-Fano lineshape) or semiconducting (Lorentzian lineshape). The disorder-related mode (D peak) is a phonon mode at 1300 cm−1 and involves the resonantly enhanced scattering of an electron via phonon emission by a defect that breaks the basic symmetry of the graphene plane. This mode corresponds to the conversion of a sp2-hybridized carbon to a sp3-hybridized on the surface. Intensity of D peak measures covalent bond made with the nanotube surface. This feature does not increase as a result of surfactant or hydronium ion adsorption on the nanotube surface. Selective reaction and Raman features Selective functionalization