Investigation of solid carbon blacks using pulsed photoacoustic and double resonant Raman spectroscopy for the identification of trinitrotoluene

We report the time resolved pulsed photoacoustic (PA) spectra of different types of solid carbon blacks obtained from wood charcoal; graphite powder and diesel soot using 532 nm wavelength pulses of duration 30 ps at a repetition rate of 10 Hz. The result of the PA spectra allows us to evaluate the potential use of graphite powder for the identification of trinitrotoluene (TNT) explosive for the first time. Though, TNT has no absorption band at 532 nm (due to higher band gap i.e. 2.7 eV), but its mixture in graphite matrix might reduce the band gap and enable it to absorb 532 nm wavelength due to pi-orbital coupling between graphite and TNT molecules. This is clearly observed concerning downshift in the Raman spectra of the mixture. Further, it is also explained using momentum exchange mechanism due to acoustic phonon waves in their common bands of Raman spectra. Finally, we have studied the different weight percentage of TNT explosive to generalize the response of PA signal.