Matrix isolation/aggregation of sodium atoms and molecules formed in a supersonic nozzle beam

Abstract

Preformed sodium molecules and atoms from a supersonic nozzle beam were deposited in krypton matrices on a sapphire window at 4 K. Matrix absorption spectroscopy was performed in the wavelength range 400-800 nm using a double-beam arrangement. Simultaneously the relative concentrations of molecules and atoms in the molecular beam were determined by mass spectrometry. Matrix/guest ratios were varied between 150: 1 and 30 000: 1 and a lower bound of ≈ 20 000: 1 was found necessary to prevent matrix aggregation processes. The atomic transitions were identified at around 590 nm and absorption bands at 655 nm and 473 nm assigned to the Na2 2 A ← X and B ← X transitions, respectively. Further bands of Na 3 and Na 4 appear between 630 and 780 nm in partial agreement with the gas phase spectra. Spectroscopic changes during matrix annealing indicate growth of sodium aggregates via small clusters. Correlation of the optical and mass spectrometric measurements proves that preformed Na x molecules can be matrix isolated as such.