Absorption spectrum in the wings of the potassium second resonance doublet broadened by helium

We have measured the reduced absorption coefficients occurring in the wings of the potassium 4S-5P doublet lines at 404.414 nm and at 404.720 nm broadened by helium gas at pressures of several hundred Torr. At the experimental temperature of 900 K, we have detected a shoulder-like broadening feature on the blue wing of the doublet which is relatively flat between 401.8 nm and 402.8 nm and which drops off rapidly for shorter wavelengths, corresponding to absorption from the X doublet Sigma+ state to the C doublet Sigma+ state of the K-He quasimolecule. The accurate measurements of the line profiles in the present work will sharply constrain future calculations of potential energy surfaces and transition dipole moments correlating to the asymptotes He-K(5p), He-K(5s), and He-K(3d).Comment: 2 figure

Soft Argon–Propane Dielectric Barrier Discharge Ionization

Dielectric barrier discharges (DBDs) have been used as soft ionization sources (DBDI) for organic mass spectrometry (DBDI-MS) for approximately ten years. Helium-based DBDI is often used because of its good ionization efficiency, low ignition voltage, and homogeneous plasma conditions. Argon needs much higher ignition voltages than helium when the same discharge geometry is used. A filamentary plasma, which is not suitable for soft ionization, may be produced instead of a homogeneous plasma. This difference results in N₂, present in helium and argon as an impurity, being Penning-ionized by helium but not by metastable argon atoms. In this study, a mixture of argon and propane (C₃H₈) was used as an ignition aid to decrease the ignition and working voltages, because propane can be Penning-ionized by argon metastables. This approach leads to homogeneous argon-based DBDI. Furthermore, operating DBDI in an open environment assumes that many uncharged analyte molecules do not interact with the reactant ions. To overcome this disadvantage, we present a novel approach, where the analyte is introduced in an enclosed system through the discharge capillary itself. This nonambient DBDI-MS arrangement is presented and characterized and could advance the novel connection of DBDI with analytical separation techniques such as gas chromatography (GC) and high-pressure liquid chromatography (HPLC) in the near future