Doppler-free Spectroscopy of Buffer-Gas-Cooled Calcium Monohydroxide

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2023-06, Vol.127 (21), p.4758-4763
• Main Authors: Miyamoto, Yuki, Tobaru, Reo, Takahashi, Yuiki, Hiramoto, Ayami, Iwakuni, Kana, Kuma, Susumu, Enomoto, Katsunari, Baba, Masaaki
• Format: Article
• Language: English
• Subjects: A: New Tools and Methods in Experiment and Theory
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.2c08565

In this study, we report the Doppler-free spectra of buffer-gas-cooled CaOH. We observed five Doppler-free spectra containing low-J Q1 and R12 transitions, which were only partially resolved by previous Doppler-limited spectroscopies. The spectra frequencies were corrected using the Doppler-free spectra of iodine molecules; accordingly, the uncertainty was estimated to be below 10 MHz. We determined the spin–rotation constant in the ground state, which agrees with the values reported in the literature obtained based on millimeter-wave data within 1 MHz. This suggests that the relative uncertainty is much smaller. The present study demonstrates the Doppler-free spectroscopy of a polyatomic radical and the broad applicability of the buffer gas cooling method to molecular spectroscopy. CaOH is the only polyatomic molecule that can be directly laser-cooled and trapped in a magneto-optical trap. High-resolution spectroscopy of such molecules is useful for establishing efficient laser cooling schemes of polyatomic molecules.