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.