science-softCon uv/vis+ photochemistry database;	www.photochemistry.org; (C) science-softCon 2019

Substance: methane					Other Names: 

Formula: CH4						CAS-No.: 74-82-8

Study: photolysis, quantum yields

                
Authors: B. Gans, S. Boyé-Péronne, M. Broquier, M. Delsaut, S. Douin, C.E. Fellows, P. Halvick, J.-C. Loison, R.R. Lucchese, D. Gauyacq 

Title: Photolysis of methane revisited at 121.6 nm and at 118.2 nm: quantum yields of the primary products, measured by mass spectrometry

Journal/Source: Phys. Chem. Chem. Phys., 13, 8140-8152, (2011); DOI: 10.1039/C0CP02627A


Data: 

Energy/Wavelength range: 121.6 nm and 118.2 nm

Resolution: 

Temperature: 

Temperature dependence: 

Pressure/Concentration: 

Phase: gas

pH:


Comments: Methane photolysis has been performed at the two Vacuum UltraViolet (VUV) wavelengths, 121.6 nm and 118.2 nm.
The radical products, CH3(X), CH2(X), CH2(a) and C(1D), have been selectively probed by mass spectrometry.
By adding the interpolated values of CH quantum yields measured by Rebbert and Ausloos [J. Photochem., 1972, 1, 171-176], a complete set of fragment 
quantum yields has been derived for the methane photodissociation at 121.6 nm, with carefully evaluated 1sigma uncertainties: Phi[CH3(X)] = 0.42 ± 0.05, 
Phi[CH2(a)] = 0.48 ± 0.05, Phi[CH2(X)] = 0.03 ± 0.08, Phi[CH(X)] = 0.07 ± 0.01. These new data have been measured independently of the H atom fragment quantum yield, subject to many controversies in the literature. From our results, we evaluate Phi(H) = 0.55 ± 0.17 at 121.6 nm. The quantum yields for the 
photolysis at 118.2 nm differ notably from those measured at 121.6 nm, with a substantial production of the CH2(X) fragment: Phi[CH3(X)] = 0.26 ± 0.04, 
Phi[CH2(a)] = 0.17 ± 0.05, Phi[CH2(X)] = 0.48 ± 0.06, Phi[CH(X)] = 0.09 ± 0.01, Phi(H) = 1.31 ± 0.13.

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