Knowledge Bank

Absorption cross-sections of the C-H stretching overtones of benzene, chlorobenzene, 1,2-dichlorobenzene, and toluene have been measured in the NIR (5970 to 6135 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$) using CW-Cavity Ringdown Spectroscopy. The wavelength-dependent absorption cross-sections were obtained with both an external cavity diode laser and a free space DFB diode laser. Low-pressure samples (0.01 to 2.0 Torr) were introduced into an evacuated cavity. The experimental room temperature absorption cross-sections obtained for these four volatile organic compounds were found to vary in intensity from approximately are 1.2 x $10-22$ to 6.9 x $10-21$ cm $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$, depending on the wavelength and molecular structure. The substitution of 1 or 2 Cl atoms causes a spectral shift to the blue relative to the benzene peak, whereas the substitution of a methyl group causes a red shift.