[Study on decomposition products of methanol in AC discharge by spectroscopy]

The intermediate decomposition products of methanol (CH3OH) in an AC discharge were diagnosticated via concentration modulation spectroscopy. Several main vibrational bands of CO Angström beta 1 sigma+ -alpha 1pi system, CH alpha 2 delta-X2pi system at 430 nm and beta 2 sigma- -X2pi at 390 nm, as well as CHO (329.82 nm), CH2O (369.8 nm), CH3O (347.8 nm) and Balmer series spectra of H atom were identified in the region between 300 and 670 nm. Furthermore, the dependences of the emission spectral intensities of the intermediate decomposition products on the discharge voltage and parent gas pressure were investigated in detail. The experiments indicated that the relative population ratio of CO (beta 1 sigma+) and H increases with increasing discharge voltage more quickly than that of CH (alpha 2 delta). Several possible reaction passages were given and discussed. Additionally, the vibrational and rotational temperatures of CH (alpha 2 delta) were determined to be about 4200 and 1100 K respectively, and the vibrational temperatures of CO (beta 1 sigma+) were determined to be about 2500 K by analyzing the intensity distribution using LIFEBASE computer program. The decomposition mechanism of methanol in the discharge plasma was discussed as well.