Abstract
Abstract Penning ionization of amides (formamide, acetamide, and thioacetamide) upon collision with He*(2 3 S) metastable atoms was studied by collision-energy-resolved Penning ionization electron spectroscopy. Partial ionization cross sections were found to be larger for ionization from molecular orbitals having electron density around the CO and CS groups. Collision energy dependence of partial ionization cross sections indicates that interaction potentials are highly anisotropic between He*(2 3 S) atoms and amides. The larger negative collision energy dependence of σ CO bands as compared to π bands shows that attractive interactions are larger around the oxygen atom for the in-plane direction rather than the out-of-plane direction. On the contrary, the larger negative collision energy dependence for ionization from non-bonding sulfur orbitals as compared to the σ CS band indicates that an attractive interaction around the sulfur atom was larger for in-plane or out-of-plane directions vertical to the CS axis. Weak interactions around the nitrogen atoms are different from the strong attractive interaction around the ‘lone pair’ orbital region of amines.
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