Reactions of Ar+ with H2, N2, O2, and CO at 20, 30, and 70 K

Photodissociation of [Ar-N2]+ induced by near-IR femtosecond laser fields by ion-trap time-of-flight mass spectrometry

Photodissociation of [Ar-N₂]⁺ induced by a near-IR (800 nm) femtosecond laser pulse is investigated using ion-trap time-of-flight mass spectrometry. The intra-complex charge transfer proceeding in the course of the decomposition of the electronically excited Ar⁺(²P_3/2)⋯N₂(X¹Σ_g ⁺), prepared by the photoexcitation of the electronic ground Ar(¹S₀)⋯N₂ ⁺(X²Σ_g ⁺), is probed by the ion yields of Ar⁺ and N₂ ⁺. The yield ratio γ of N₂ ⁺ with respect to the sum of the yields of Ar⁺ and N₂ ⁺ is determined to be γ = 0.62, which is much larger than γ ∼ 0.2 determined before when the photodissociation is induced by a nano-second laser pulse in the shorter wavelength region between 270 and 650 nm. This enhancement of γ at 800 nm and the dependence of γ on the excitation wavelength are interpreted by numerical simulations, in which the adiabatic population transfer from Ar⁺(²P_3/2)⋯N₂(X¹Σ_g ⁺) to Ar(¹S₀)⋯N₂ ⁺(X²Σ_g ⁺) at the avoided crossings is accompanied by the vibrational excitation in the N₂ ⁺(X²Σ_g ⁺) moiety followed by the intra-complex vibrational energy transfer from the N₂ ⁺(X²Σ_g ⁺) moiety to the intra-complex vibrational mode leading to the dissociation.

Reaction kinetics at very low temperatures: laboratory studies and interstellar chemistry

Studies of gas-phase processes at temperatures down to 10 K have recently blossomed, largely through application of the CRESU (cinétique de réaction en ecoulement supersonique uniforme) technique. The results are of considerable relevance to the synthesis of molecules in dense interstellar clouds, demonstrating that the models developed to explain the observed molecular abundances must be expanded to include reactions between electrically neutral species. In addition, the experimental results have stimulated theoretical efforts to describe the factors that control the rates of such low-temperature reactions. In this Account, the CRESU method is described and the relevance of the results discussed.