This study brings initial insight on the characterization of the gas chemical composition in a dielectric barrier discharge by Fourier-Transformed InfraRed (FTIR) absorption spectroscopy. Capitalizing on a double path of the IR beam, measurements were performed in 5 cm-long, 2 mm-gap plasma. As the IR beam crosssection in the plasma was 2x2 mm², a translation system was used to scan the plasma along the direction of the gas flow with a 2 mm spatial resolution. In the case of Ar-SiH4(67ppm)-NH3(133ppm) glow-mode DBD, all IR spectra peaks from 6000 to 800 cm -1 are related to vibrations of Si-H from SiH4 and N-H from NH3. Here, the N-H vibration is observable but non-quantifiable. At 50 kHz excitation, the absolute concentration of SiH4 was measured on different positions and different power values in continuous and modulated modes. In the absence of powder formation in the plasma and for an initial density of 1.6.10 15 cm -3 , all the measurements are fitted by the same exponential decay leading to an energy of 42eV per dissociated molecule of SiH4. The presence of powders in the plasma reduces SiH4 dissociation rate by a factor larger than 4.