Absolute Measurements of Emission Cross-Sections for Dissociative Excitations of H₂O by Electron-Impact with Crossed-Beam Apparatus and High Sensitive Quartz Spring Balance

Absolute measurements of the emission cross-sections for the A - X band-spectrum of OH and the H β line in the dissociative excitation processes of H 2 O by electron-impact have been carried out by means of the crossed-beam technique, with the aid of a high sensitive spring balance made of fused quartz. The spring has a tiny pan, which is surrounded by a specially designed trap of liquid nitrogen. The spring words well for direct intensity measurements of the water molecular beam, because the condensation coefficient of H 2 O on ice is large enough at lower temperatures. The following results have been obtained; (4.2±2.1)×10 -18 cm 2 for the H β transition, and (7.1±3.5)×10 -18 cm 2 for the OH ( A , 2 Σ + - X , \(²\)) transition, at 300 eV respectively.