河野 淳也

Abstract In this study, we used atmospheric-pressure droplet laser-ablation mass spectrometry to elucidate the chemical pathways induced by UV-laser irradiation of carbon tetrachloride (CCl4) droplets containing various alcohols. We focused on the reaction dynamics following the laser-induced generation of trichloromethyl radicals (CCl3) and ions (CCl3+) in the microdroplets. Mass spectrometric analysis revealed that CCl3+ initiated sequential substitution reactions. With phenol, sequential substitution occurred, resulting in the formation of mono-, di-, and trisubstituted ions. Conversely, methanol and ethanol exclusively yielded trisubstituted species [C(OR)3+], regardless of the concentration, which we attributed to the formation of alcohol aggregates in the CCl4 solution. For bulkier alcohols, steric hindrance suppressed substitution, and this favored CCl3-mediated hydrogen abstraction followed by radical coupling. Isotope-labeling experiments with ethanol revealed a higher abundance of coupling products derived from beta-site abstraction than from alpha-site abstraction, suggesting distinct kinetic preferences in the coupling step. These findings demonstrate that the microdroplet environment and molecular aggregation dictate the selectivity of laser-induced organic synthesis. This knowledge provides a basis for developing novel pulsed-laser-based synthetic methodologies.

We investigated the temporal dynamics of multi-order stimulated Raman scattering (SRS) generated in single and colliding liquid droplets of carbon tetrachloride. Liquid droplets function as high-quality factor (Q) optical cavities via whispering-gallery modes, facilitating intense nonlinear optical processes. Using a 532 nm pulsed laser, we conducted a comprehensive shot-to-shot analysis of over 103 SRS waveforms. We observed that the generation time of multi-order SRS in a single droplet was delayed by 10–20 ns relative to the incident laser pulse. Our results revealed a sequential buildup process in which the (i − 1)th order SRS pumped the ith order SRS, resulting in progressive time delays for successive order SRS. In contrast, colliding droplets exhibited a significantly shorter generation time and higher efficiency than single droplets. A numerical multi-order SRS generation model was employed to fit the experimental temporal profiles, yielding a Q of ∼3 × 107 and 5 × 106 for single and colliding droplets, respectively. The lower Q in colliding droplets, arising from the high surface curvature of the disk-like mixing region, enhances the coupling efficiency between the incident field and droplet cavity. These findings clarify the dynamic buildup of nonlinear processes in microspherical cavities and demonstrate that colliding droplets can function as highly efficient, tunable cavities for advanced molecular spectroscopy and interface analysis.

Abstract Guanine (G) molecules form a stable tetramer with a metal ion called a G-quartet. We observed G-quartets by using atmospheric pressure droplet Infrared-laser ablation mass spectrometry, which enables us to analyze the abundance of chemical species in solutions. We estimated the association constants of Gn and M+ (M+ = Li+, Na+, and K+) from the intensities of G1–5H+ and G1–4M+ in the obtained mass spectra. The larger association constants of G4 than those of Gn (n ≠ 4) indicate the stability of G-quartets.