Absolute cross sections of electron attachment to molecular clusters: Part I. Formation of (CO₂) ⁻_N

Abstract

A procedure of determining absolute cross section σ⁻ of electron attachment to (CO₂)_N clusters at pair collisions in crossed beams is suggested. The cross section is measured as a function of energy (E = 0.1–50 eV) and of cluster mean size N in a beam $(\bar N = 2 - 4000 molecules)$. It is found that, even at $\bar N > 200$ and E ≤ 3 eV, σ⁻ is equal to, or larger than, 7 × 10⁻¹³ cm², i.e., by more than one order of magnitude exceeds the maximal cross section of CO₂ ionization by electron impact. The dependences σ⁻ $(\bar N,E)$ have two wide continua at E ≤ 5.2 eV and E ≥ 6.9 eV, which correlate well with known functions of CO₂ electron-impact-induced excitation. These continua are attributed largely to formation of (CO₂) ⁻_N ions during electron thermalization and solvation in the clusters. At E → 0, the polarization capture of an incident electron by the cluster leads to a sharp increase in cross section σ⁻(E). From the dependences σ⁻ $(\bar N,E)$ measured, the thermalization and sovation probabilities for electrons with E ≤ 0.8 eV and the rate of electron energy loss in the cluster are found.