Polarisation and angular correlation studies of the 63P1-61SO intercombination line of mercury by electron impact

Abstract

A crossed-beam was used to measure the polarisation of the 63P1 – 61S0 intercombination line (λ = 253.7 nm) of mercury, excited by electron impact, in the energy range from threshold at 4.89 eV to 7.5 eV. An isotope cell was used to absorb selectively the radiation emitted from odd isotopes with non-zero nuclear spins and, hence, eliminate the effect of hyperfine structure on the polarisation. These results are compared with the polarisation of the radiation when the effect of hyperfine structure was present. The degree of polarisation is found to increase after the elimination of the hyperfine effect. A delayed coincidence technique was utilised to measure the electron-photon coincidence rates for the excitation/de-excitation process, 61S0 ‎‎→ 63P1 → 61S0, in mercury by electron impact. The electrons, inelastically scattered with an energy loss of 4.89 eV, were detected in coincidence with photons emitted from the subsequent decay of the 63P1 state. These observations were made for fixed electron energies of 5.5 eV and 6.5 eV at electron scattering angles of 50o and 70o. The vector polarisation and coherence parameters of the coincident photon radiation are evaluated in terms of the Stokes parameters to determine the coherent nature of the excitation process. Although the coherence of the above excitation/de-excitation process increased after the elimination of the hyperfine effect, the process is still partially coherent.