High-resolution spectroscopy of buffer-gas-cooled phthalocyanine

For over five decades, studies in chemical physics and physical chemistry have aimed to understand molecular quantum properties, but high-resolution rovibronic spectroscopy has largely been limited to small, simple systems due to the difficulty of preparing large, complex molecules in sufficiently cold and abundant gas-phase samples. Here, high-resolution rovibronic spectroscopy of large gas-phase molecules, specifically free-base phthalocyanine (FBPc), is demonstrated. The results indicate that buffer-gas cooling is effective for large molecules introduced via laser ablation. High-resolution electronic spectroscopy combined with experimental and theoretical analyses enables better understanding of molecular quantum states and guides quantum chemical calculations of large molecules. In this work, helium buffer-gas cooling at cryogenic temperatures allows observation of rotationally structured visible spectra of FBPc; comparison with simulations shows both rotational and translational temperatures below 10 K. These findings highlight the feasibility of high-resolution studies on large molecules and provide benchmarks for theory. A contemporaneous supersonic-jet study reported similar spectral features but reached different conclusions regarding transition type, motivating further work.

Yuki Miyamoto, Reo Tobaru, Yuiki Takahashi, Ayami Hiramoto, Kana Iwakuni, Susumu Kuma, Katsunari Enomoto, Masaaki Baba