Rotationally Resolved Predissociation Spectrum of the 1⁵Φ ← X⁵Δ Rovibronic Band of FeH.

Area of Science:

• Astrochemistry
• Molecular Spectroscopy
• Quantum Chemistry

Background:

• The iron hydride cation (FeH+) is a hypothesized molecule in cool interstellar environments.
• Its neutral counterpart (FeH) is detected in stellar atmospheres.
• Lack of laboratory data has hindered FeH+ identification in space.

Purpose of the Study:

• To obtain and analyze the first rotationally resolved photodissociation spectrum of gas-phase FeH+.
• To provide essential laboratory data for identifying FeH+ in astronomical observations.
• To elucidate the electronic structure and predissociation mechanisms of FeH+.

Main Methods:

• Acquisition of a rotationally resolved photodissociation spectrum of FeH+ in the 18550-18830 cm⁻¹ range.
• High-level computational chemistry: multireference and coupled cluster calculations.
• Rovibrational spectra simulations for spectral assignment.

Main Results:

• The 1⁵Φ ← X⁵Δ electronic transition of FeH+ was rotationally resolved and assigned.
• Predissociation broadening was observed due to curve crossings with repulsive states.
• The photodissociation cross-section was found to be low (< 5 × 10⁻²⁰ cm²).

Conclusions:

• The laboratory spectrum of FeH+ does not match observations of HD 183143.
• The predicted spectral onset is above 1300 GHz, inaccessible to ground-based telescopes.
• Further laboratory data and theoretical refinements are needed for astronomical identification.