Total Cross Sections for Collisional Quenching of H(2s) Atom in Molecular Targets

Total cross sections σ t for collisional quenching of H(2s) atoms in H 2 , N 2 , O 2 , CO, CO 2 and CH 4 molecular targets have been measured in the projectile energy range from 0.2 to 3.5 keV. A H(2s) atom beam was produced by using H + –K near-resonant charge transfer collisions, and σ t 's were determined with a beam attenuation method. It is demonstrated that, in the lower energy region (<0.5 keV) where the 2s-2p de-excitation process dominates, the long-range interaction due to polarization of a target molecule is more important than that due to its permanent quadrupole moment M 2 . This result is not consistent with theoretical treatments where M 2 is assumed to be more effective than the polarization. In the higher energy region (\({}0.5\) keV), the σ t curves behave in complex manners due to opening of other quenching processes such as electron-loss and electron-capture processes.