A Chemiluminescent and Laser-Induced Fluorescent Probe of a New Low-Lying A′Ω = 1 State of Gaseous AgF

Abstract

A new A′ 1 (Ω = 1) state of AgF at the fringes of the visible region has been excited and analyzed. The chemiluminescence from this state, which is located ∼4300 cm−1 below the previously known lowest excited A 0+ state, is observed for the first time in a beam-gas reaction where silver molecules, Agx, are reacted with either atomic or molecular fluorine. Using pulsed laser-induced fluorescence, two vibrational bands (v′, v″) = (0, 0) and (1, 0) have been rotationally resolved and electronic and rotational assignments have been obtained. Molecular constants which can reproduce the observed data with a standard deviation of 0.1 cm−1, the RKR potential energy curve, and the Franck-Condon factors for the A′ 1-X1Σ+ transition have been determined. The internal energy distributions of the reaction product AgF molecules are studied by vibrational intensity analysis and rotational simulation calculations. The possible reaction paths to produce the excited A′, state from either the four-center Ag2′ + F2 or Agx (x ≥ 3) + F reactions and the formation of ground state AgF molecules are discussed through consideration of reactant-product correlations and energetics. The dissociation energy of the newly observed A′ 1 state is 4649 ± 1400 cm−1. The observation of this low-lying Ω = 1 state indicates the existence of similar stable Ω = 1 states for the remaining silver halides, all of which should readily absorb visible photons. Their existence, which may have implications for the detailed understanding of the photographic process, provides intermediate states for multiple-resonance laser excitation and multiphoton laser ionization.