Laser-induced Fluoresence of Linear-Chain Molecular Ions in Neon Matrices

Abstract

The $\tilde{A}^{2}\Pi \leftrightarrow \tilde{X}^{2}\Pi$ transitions of the ions $H-(C\equiv C)_{n}-H^{+} (n=3-5)^{a}, H-(C\equiv C)_{n}-C\equiv N^{+} (n=2-3)^{b}$, and $N \equiv C^{-}(C\equiv C)_{n}-C\equiv N^{+} (n=1-3)^{c-d}$ are studied in neon matrices through Fourier-transform absorption, emission and laser excitation spectroscopies. The ions are produced from simple precursors diluted in neon using a source combining a self-igniting discharge with a pulsed supersonic expansion recently developed in our laboratory. For each of the three ion families, the red shift of the $\tilde{A}^{2}\Pi \leftrightarrow \tilde{X}^{2}\Pi$ transition with increasing chain length is quite accurately predicted by a one-dimensional particle in a box model. Stretching vibrational information for both the ground and excited states is extracted from the very sharp and well-resolved spectra. As clearly seen in our three-dimensional (emission, excitation, emission intensity) spectra, these linear-chain ions all show subsidiary emission/excitation bands for the bluer of the two discrete sites, which are best interpreted as due to the nominally forbidden ${^{2}}\Pi_{\frac{1}{2}} \leftrightarrow {^{2}}\Pi_{\frac{3}{2}}$ transitions.