Laser spectroscopy on molecular beam with a time-of-flight mass spectrometer operating in a strong magnetic field

Experimental set-up for studying effects of a strong magnetic field on a structure and a decay dynamics of molecules, was designed and constructed. A vacuum chamber, in which a molecular beam propagated, was mounted in a bore of a superconducting magnet. Laser light crossed the molecular beam in the magnetic field and excited the molecules. Fragment or parent ions produced through sequential decay processes, were extracted by an electric field parallel to the magnetic field and detected by a microchannel plate. By measuring the time-of-flight from the photo-excitation to the ion-detection, a species of ions —mass and charge state— was identified. A performance of the set-up was demonstrated using the resonance enhanced multiphoton ionization process through the X²Π-A²Σ⁺ transition of nitric oxide (NO) molecules. A mass resolution m/Δm ≥180±6 was obtained in the field up to 10 T. This was the first successful result demonstrating the sufficient mass resolution obtained by the time-of-flight technique in the strong magnetic field up to 10 T. Parent NO⁺ ions were selectively detected by the mass spectrometer and the ion current was measured as a function of the frequency of the laser light. Rotational transition lines were measured with a sufficient S/N ratio in the field up to 10 T.