Thermal electron attachment to van der Waals molecules (O2⋅N2)

Abstract

Electron attachment to van der Waals (vdW) molecules (O₂⋅N₂) has been investigated at temperatures from 77 to 373 K and N₂ densities from 2.0×10¹⁸ to 3.5×10¹⁹ molecules/cm³ using a microwave conductivity technique combined with pulse radiolysis. The initial electron attachment rate constants to O₂ and (O₂⋅N₂) are obtained as k₁=(4.2⁺¹⁷₋₃) ×10⁻⁶T^1.5 exp(−1017/T) cm³/s and k₅=(3.4±0.4)×10⁻⁴T^−1.5 exp[−(232±12)/T] cm³/s, respectively. The resonance energy for the electron attachment to (O₂⋅N₂) is reduced to 20±1 meV owing to polarization energy between O⁻₂ and N₂. The electron attachment rate constant for (O₂⋅N₂) is about 10³ times larger than that for O₂. The reason is: (i) the increase of electron density at the resonance energy for attachment; (ii) the increase of attachment cross section with decreasing the resonance energy; and (iii) that by vdW interaction partial‐wave electrons with lower angular momentum can attach to vdW molecules. Since the resonance width for the electron attachment to (O₂⋅N₂) is larger (800±100 μeV), the (O₂⋅N₂)⁻* formed is easy to ionize. Experimental results at high pressures have shown collisional detachment of electrons from (O₂⋅N₂)⁻*.