Excited States of Gaseous Ions. II. Metastable Decomposition and Predissociation of the CH+ Ion

Abstract

The slow fragmentation process (τ≃10−7sec) of the CH+ ion in a mass spectrometer can be ascribed to the superposition of several predissociation mechanisms. The potential energy curves of the CH+ ion have been calculated quantum mechanically, and for each intersection, the predissociation lifetime has been estimated on the basis of the Landau—Zener formula. Metastable ions are due to a spin-forbidden predissociation process, allowed by the spin—orbit (Hso), spin—other-orbit (Hsoo) and spin—spin (Hss) operators. These three operators are in some cases sufficient to obtain a lifetime much shorter than 10−7 sec. In order to give rise to a metastable fragmentation, the predissociation process must be slowed down, either by the tunnel effect, or because of a deviation from the Landau—Zener formula. The effect of the collisions on the predissociation processes is discussed. In some cases the mechanism of this effect involves energy transfer, while in others only a symmetry loss occurs. A strictly forbidden predissociation process, for which the matrix elements of Hso, Hsoo, and Hss are equal to zero, can only take place as a collision-induced process. Although they are characterized by a peculiar potential energy curve, exhibiting a shallow basin, the Rydberg states are not involved in the metastable decomposition.

The dissociative ionization in oxygen

“…These rules have recently been revised in cases where spin-orbit coupling has to be considered [21]. Predissociations of diatomic molecular ions with life-times of the order of 10 -6 s have been observed in sectorfield mass spectrometers as "metastable" peaks characterized by their shape, width and position at fractional mass numbers [19][20][21].…”

Transport of molecular impurities at the edge of tokamaks

“…They find that the primary product is CH, + + H (0. since this strongly influences the carbon source function in the plasma. The potential energy curves of CH given by wrquet et al [27] from reference [7] and are based on a calculation using BALDUR [9]. The arrows indicate the location of the limiter.…”

Photodissociation spectroscopy of stored CH+ and CD+ ions: Analysis of theb 3Σ−-a 3Π system

“…This storage time is sufficient for many polar molecules to internally cool by spontaneous emission until the rovibrational distribution reaches room temperature, as imposed by the surrounding blackbody radiation. 20,19 For the isoelectronic BH molecule, the predissociation step has been studied in detail, both theoretically 21 and experimentally. 18 For CH + , we have used the storage-ring technique to measure the weak photodissociation signal from ions in the ground state X 1 ⌺ + ͑v =0͒, decaying into C + and H fragments via near-threshold Feshbach resonances of the A 1 ⌸ state ͑process I in Fig.…”