Spectroscopic characterization of the a\(^3\Pi\) state of aluminum monofluoride

• Published in: arXiv.org 2022-02
• Main Authors: Walter, Nicole, Doppelbauer, Maximilian, Marx, Silvio, Seifert, Johannes, Liu, Xiangyue, Jesús Pérez Ríos, Sartakov, Boris, Truppe, Stefan, Meijer, Gerard
• Format: Article
• Language: English
• Subjects: Aluminum; Ionization; Laser cooling; Line spectra; Molecular beams; Photon scatter; Quantum chemistry; Radiative lifetime; Rotational spectra
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2112.09498

Spectroscopic studies of aluminum monofluoride (AlF) have revealed its highly favorable properties for direct laser cooling. All \(Q\) lines of the strong A\(^1\Pi\) \(\leftarrow\) X\(^1\Sigma^+\) transition around 227~nm are rotationally closed and thereby suitable for the main cooling cycle. The same holds for the narrow, spin-forbidden a\(^3\Pi\) \(\leftarrow\) X\(^1\Sigma^+\) transition around 367 nm which has a recoil limit in the micro Kelvin range. We here report on the spectroscopic characterization of the lowest rotational levels in the a\(^3\Pi\) state of AlF for \(v=0-8\) using a jet-cooled, pulsed molecular beam. An accidental AC Stark shift is observed on the a\(^3\Pi_0, v=4\) \(\leftarrow\) X\(^1\Sigma^+, v=4\) band. By using time-delayed ionization for state-selective detection of the molecules in the metastable a\(^3\Pi\) state at different points along the molecular beam, the radiative lifetime of the a\(^3\Pi_1, v=0, J=1\) level is experimentally determined as \(\tau=1.89 \pm 0.15\)~ms. A laser/radio-frequency multiple resonance ionization scheme is employed to determine the hyperfine splittings in the a\(^3\Pi_1, v=5\) level. The experimentally derived hyperfine parameters are compared to the outcome of quantum chemistry calculations. A spectral line with a width of 1.27 kHz is recorded between hyperfine levels in the a\(^3\Pi, v=0\) state. These measurements benchmark the electronic potential of the a\(^3\Pi\) state and yield accurate values for the photon scattering rate and for the elements of the Franck-Condon matrix of the a\(^3\Pi\) \(-\) X\(^1\Sigma^+\) system.