ABSTRACT
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.
ABSTRACT
For over five decades, studies in the field of chemical physics and physical chemistry have primarily aimed to understand the quantum properties of molecules. However, high-resolution rovibronic spectroscopy has been limited to relatively small and simple systems because translationally and rotationally cold samples have not been prepared in sufficiently large quantities for large and complex systems. In this study, we present high-resolution rovibronic spectroscopy results for large gas-phase molecules, namely, free-base phthalocya-nine (FBPc). The findings suggest that buffer-gas cooling may be effective for large molecules introduced via laser ablation. High-resolution electronic spectroscopy, combined with other experimental and theoretical studies, will be useful in understanding the quantum properties of molecules. These findings also serve as a guide for quantum chemical calculations of large molecules.