Theoretical Study of the Gas-Phase Chemiionization Reactions La + O and La + O₂

Abstract

The La + O and La + O 2 chemiionization reactions have been investigated with quantum chemical methods. For La + O 2 (X 3 Σ g ) and La + O 2 (a 1 ∆ g ), the chemiionization reaction La + O 2 f LaO 2 + + e -has been shown to be endothermic and does not contribute to the experimental chemielectron spectra. For the La + O 2 (X 3 Σ g ) reaction conditions, chemielectrons are produced by La + O 2 f LaO + O, followed by La + O f LaO + + e -. This is supported by the same chemielectron band, arising from La + O f LaO + + e -, being observed from both the La + O( 3 P) and La + O 2 (X 3 Σ g ) reaction conditions. For La + O 2 (a 1 ∆ g ), a chemielectron band with higher electron kinetic energy than that obtained from La + O 2 (X 3 Σ g ) is observed. This is attributed to production of O( 1 D) from the reaction La + O 2 (a 1 ∆ g ) f LaO + O( 1 D), followed by chemiionization via the reaction La + O( 1 D) f LaO + + e -. Potential energy curves are computed for a number of states of LaO, LaO* and LaO + to establish mechanisms for the observed La + O f LaO + + e -chemiionization reactions.

Systematic truncation of the virtual space in multiconfigurational perturbation theory

“…The CD-CASPT2 values are R e = 1.855 Å and e = 803 cm −1 , respectively, in excellent agreement with Ref. 35. With 40% truncation, FNO-CASPT2 introduces a negligible error in the computed equilibrium distance ͑R e = 1.859 Å͒ and predicts a relatively accurate frequency of e = 759 cm −1 .…”

“…Spectroscopic constants of LaO n and LaO n + "n =1,2… An account on the mechanisms of La+ O and La+ O 2 chemionization reactions studied at the CASSCF/CASPT2 level of theory was recently given by Todorova et al 35 In the present work, spectroscopic constants of LaO n and LaO n + ͑n =1,2͒ are reproduced by employing FNO-CASPT2, in order to understand the reliability and the limits of this method. For consistency of the results, we employ the same basis sets ͑ANO-RCC of quintuple-quality͒, active spaces, geometries as in the previous study.…”

“…For consistency of the results, we employ the same basis sets ͑ANO-RCC of quintuple-quality͒, active spaces, geometries as in the previous study. 35 The only difference is the use of the CD approximation for the ERIs. The value of the decomposition threshold ͑here 10 −8 ͒ has been chosen to make sure that the CD-CASPT2 results are nearly identical to those reported in Ref.…”

“…The value of the decomposition threshold ͑here 10 −8 ͒ has been chosen to make sure that the CD-CASPT2 results are nearly identical to those reported in Ref. 35. They allow for a neat inspection of the error introduced by the FNO approximation.…”

The chemiionization reactions Ce + O and Ce + O2: Assignment of the observed chemielectron bands

“…In a recent publication, the chemiionization reactions that occur for the La + O( 3 P), La + O 2 (X 3 Σ), and La + O 2 (a 1 Δ g ) reaction conditions have been established by quantum chemical methods 1. It has been shown that for La + O 2 (X 3 Σ) and La + O 2 (a 1 Δ g ), the chemiionization reaction La + O 2 → LaO + e − is endothermic and does not contribute to the experimental chemielectron spectra.…”