Experimental and theoretical study of Penning ionisation of H₂O by metastable helium He(2³S)

The Possible Role of Penning Ionization Processes in Planetary Atmospheres

“…The analysis of the obtained results suggests the selective role of a quite pronounced anisotropic attraction that controls the stereodynamics in the entrance channels of the analyzed systems. In the case of He * and Ne * -H2O autoionizing collisions, we were able to confirm the presence of a strong anisotropic interaction, after previous experimental and theoretical evidences by Ohno et al [27], Haug et al [28], Bentley [29], and Ishida [30], respectively. In particular, we rationalized our experimental findings, taking into account the critical balancing between molecular orientation effects in the intermolecular interaction field and the ionization probability.…”

“…A still quite strong attractive behavior drives the Ne * -H2O collisions, while the corresponding attraction in the Ne * -H2S collisions appears to be about 40% smaller than in the case of water. This consideration comes from the suggestion by Haug et al [28], who noted that the energy shift εA can be used as a proper indication of the depth of the attractive potential well of the interaction between the colliding particles in the entrance channel. This suggestion is reasonable considering the weaker attraction in the exit channel due to the very low polarizability of neon atoms (0.…”

Intermolecular potential energy surfaces for the interaction between H 2 X (X O, S) and a metastable Ne * ( 3 P 2,0 ) atom

“…In particular, the analysis of the obtained results shows the evidence of a quite pronounced anisotropy of attraction that controls the stereo-dynamics in the entrance channels of the analyzed systems. In the case of He * -and Ne * -H 2 O autoionizing collisions, we were able to confirm by a preliminary analysis the presence of a strong anisotropic interaction, after previous experimental and theoretical results by Ohno et al [8], Haug et al [9], Bentley [10], and Ishida [11]. In particular, we rationalized our experimental findings taking into account the critical balancing between molecular orientation effects in the intermolecular interaction field and the ionization probability.…”

Collision-energy-resolved Penning ionization electron spectroscopy of OCS with He*(23S) metastable atoms

“…Similarly, the most attractive well was calculated on the bisector plane for the lone pair direction in the case of He à (2 3 S)-H 2 O [27]. It should be noted that negative peak energy shift values for band 1 (3p (S 3p -O 2p ), DE ¼ À50 AE 10 meV) and band 4 (8rðr CO ), DE ¼ À25 AE 15 meV) are consistent with the large well depth around the S atom (122 meV) and O atom (71 meV) and the direction of the most attractive well around the O atom.…”