Photodissociation Spectroscopy of Stored CH+ Ions: Detection, Assignment and Close-Coupled Modeling of Near-Threshold Feshbach Resonances

Published

November 1, 2002

Author(s)

U Hechtfischer, Carl J. Williams, J Lange, J Linkemann, D Schwalm, R Wester, A Wolf, D Zajfman

Abstract

We have measured and theoretically analyzed a photodissociation spectrum of the CH⁺ molecular ion in which most observed energy levels lie within the fine-structure splitting of the C⁺ fragment and predissociate, with the observed irregular lineshapes and dipole-forbidden transitions indicating that non-adiabatic interactions lead to multichannel dynamics. The molecules were prepared in low rotational levels J = 0-9 of the vibrational ground state X¹Σ⁺ (υ¹¹ = 0) by storing a CH⁺ beam at 7.1 MeV in the heavy-ion storage ring TSR for up to 30 s, which was sufficient for the ions to rovibrationally thermalize to room temperature by spontaneous infrared emission. The internally cold molecules were irradiated with a dye laser at photon energies between 31600-33400 cm^-1, and the resulting C⁺ fragments were counted with a particle detector. The photodissociation cross section displays the numerous Feshbach resonances between the two C⁺ fine-structure states predicted by theory for low rotation. The data are analyzed in two steps. First, from the overall structure of the spectrum, by identifying branches, and by a Le Roy-Bernstein analysis of level spacings we determine the dissociation energy D0 = (32946.7 1.1) cm ^-1 (with respect to the lower fine-structure limit) and assign the strongest features to the vibrational levels υ/ = 11-14 of the dipole-allowed A1 II state, but the majority of the 66 observed resonances cannot be assigned in this way.

Citation

Journal of Chemical Physics

Volume

117

Issue

No. 19

Pub Type

Journals

Keywords

feshbach resonances, photodissociation spectroscopy

Citation

Hechtfischer, U. , Williams, C. , Lange, J. , Linkemann, J. , Schwalm, D. , Wester, R. , Wolf, A. and Zajfman, D. (2002), Photodissociation Spectroscopy of Stored CH⁺ Ions: Detection, Assignment and Close-Coupled Modeling of Near-Threshold Feshbach Resonances, Journal of Chemical Physics (Accessed April 20, 2024)