Photochemical properties of a potential interstellar dust precursor: the electronic spectrum of SiO.

Silicon oxide compounds are considered as precursors for silicon-based interstellar dust grains which consist mainly of silica and silicates. Knowledge of their geometric, electronic, optical, and photochemical properties provides crucial input for astrochemical models describing the evolution of dust grains. Herein, we report the optical spectrum of mass-selected SiO cations recorded in the 234-709 nm range by means of electronic photodissociation (EPD) in a quadrupole/time-of-flight tandem mass spectrometer coupled to a laser vaporization source.

The Electronic Spectrum of Si.

The optical spectrum of Si is presented. The two electronic band systems observed near 430 and 270 nm correspond to the two lowest optically allowed transitions of Si assigned to Σ(I) ← XΣ and Σ(II) ← XΣ. The spectra were measured via photodissociation spectroscopy of mass-selected ions at the level of vibrational resolution, and the determined spectroscopic constants provide detailed information about the geometric and electronic structure, establishing molecular constants of this fundamental diatomic cation that enable astrophysical detection on, for example, hot rocky super-Earth-like exoplanets.

Near-Infrared Spectrum of the First Excited State of Au.

Au is a simple but crucial model system for understanding the diverse catalytic activity of gold. While the Au ground state (X Σ ) is understood reasonably well from mass spectrometry and computations, no spectroscopic information is available for its first excited state (A Σ ). Herein, we present the vibrationally resolved electronic spectrum of this state for cold Ar-tagged Au cations.