Matrix Isolation of Ions and Ion Pairs: Using Pulsed Laser Deposition of Non-Volatile Halides and Pseudohalides

Abstract

The vaporization of high melting compounds for matrix-isolation spectroscopic investigations has always been a challenging experimental endeavor. Here, pulsed laser deposition is used to vaporize non-volatile halides and pseudohalides for subsequent codeposition of the ablation products with an excess of matrix gases. This method is shown to yield good results in a fraction of the time compared to Knudsen effusion and, more importantly, allows for the isolation of free anions. Pulsed laser deposition of alkali fluorides and chlorides (MF and MCl, M= Li-Cs) and their co-deposition with dihalogen (F2 and Cl2) led to the observation of new vibrational bands of free F3– and some alkali ion pairs (MF3 and MCl3) in solid neon and the first observation of free Cl3–. Matrix isolation of laser ablation products of the pseudohalide KCN yielded, among a variety of polycarbon and polynitrogen compounds, the novel ion pairs KC3 and KN3. Molecular potassium azide (KN3) was shown to exist as a side-on and an end-on isomer. As a further developement of the plain salt ablation, it was possible to investigate molecular alkali ion pairs of the tetrafluorido aurate (AuF4–) by co-deposition of laser-ablated MF/AuF3 mixtures in solid neon matrices. All results were validated by high-level quantum-chemical calculations and are here presented in the context of the present state of research.