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Abstract
Threshold photodetachment spectroscopy has been performed on the molecular anion CN- at both 16(1) K and 295(2) K in a 22-pole ion trap and at 295(2) K from a pulsed ion beam. The spectra show a typical energy dependence of the detachment cross section yielding a determination of the electron affinity of CN to greater precision than has previously been known at 31 163(16) cm-1 [3.864(2) eV]. Allowed s-wave detachment is observed for CN-, but the dependence of the photodetachment cross section near the threshold is perturbed by the long-range interaction between the permanent dipole moment of CN and the outgoing electron. Furthermore, we observe a temperature dependence of the cross section near the threshold, which we attribute to a reduction of the effective permanent dipole due to higher rotational excitation at higher temperatures.
Highlights
Molecule–photon and molecule–electron collisions are a fundamental process in many physical and chemical systems and are prevalent in areas such as atmospheric chemistry and astrochemistry and technical environments such as semiconductor manufacture, combustion chemistry, and fusion plasmas
Allowed s-wave detachment is observed for CN−, but the dependence of the photodetachment cross section near the threshold is perturbed by the long-range interaction between the permanent dipole moment of CN and the outgoing electron
Threshold photodetachment of CN− (X1Σ+) + hν → CN (X2Σ+) + e− has been measured at both 16(1) K and 295(2) K in our 22pole ion trap and at 295(2) K from the pulsed ion beam in our velocity map imaging (VMI) setup
Summary
Molecule–photon and molecule–electron collisions are a fundamental process in many physical and chemical systems and are prevalent in areas such as atmospheric chemistry and astrochemistry and technical environments such as semiconductor manufacture, combustion chemistry, and fusion plasmas. The cross section for threshold photodetachment is in general well described by a Wigner-type law, the shape of which is determined by the angular momentum taken away by the outgoing electron. For the case in which the dipole strength sufficiently dominates the electronic angular momentum, it has been shown that the detachment cross section yields an oscillatory behavior at the threshold. For an atom or non-polar molecule, the exponent P on the Wigner threshold law is equal to l + 1/2, where l is the angular momentum taken away by the outgoing electron.
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