Contribution of the 4p sublevel to the Balmer-β emission intensity from H (n=4) produced in electron-H₂, CHF₃, CH ₄ and C₃H₈ collisions as studied by photon-photon coincidence experiments

The ratio of the Balmer-β emission intensity from the 4p sublevel to the total Balmer-β emission intensity from H(n=4) produced in electron-H₂, CHF₃, CH₄ and C₃H ₈ collisions has been determined by carrying out Balmer-β-Lyman- α coincidence measurements as a function of the incident electron energy. As a result, the 4p ratio in these molecules has been found to be about 14% at an incident electron energy of 100 eV and identical in all molecules. There is a significant difference in the dependence of the 4p ratio on the incident electron energy; for example, the 4p ratio in the CHF₃ case decreases to 0% at 30 and 35 eV and increases to 90% at 25 eV; in contrast, that in the C₃H₈ case is 0% at 37 and 40 eV and 13% at 33 eV. Such dramatic dependence cannot be explained on the basis of the Stark effect caused by stray electric fields and by the partial polarization of the Balmer-β and Lyman-α emissions. The dissociation through the neutral superexcited states of these molecules causes the dramatic dependence.