Overtone Excitation of Nitrogen Molecules via Stimulated Raman Pumping

Nitrogen bond activation is a pivotal process in chemistry, with bond excitation being fundamental to understanding the underlying mechanisms, making the preparation of molecules in specific quantum states crucial. Here we report the first overtone excitation of the N₂ molecule from X¹Σ_g⁺(v = 0, j = 0, 1, and 2) to X¹Σ_g⁺(v = 2, j = 0, 1, 2, and 3) using the stimulated Raman pumping (SRP) method in a pulsed molecular beam. N₂ was detected using 2+1 resonance-enhanced multiphoton ionization through the a″¹Σ_g⁺ state. An excitation efficiency of 4% was achieved within the excitation region in which the SRP laser intensity was saturated, indicating the low cross-sectional nature of the process. The SRP detuning spectra for different branches were measured, and the excited N₂ [X¹Σ_g⁺(v = 2)] was further used to access various vibrational states of a″¹Σ_g⁺, enabling the determination of its vibrational constants. This research opens up new opportunities for studying the specific high vibrational excitation of nitrogen in reactions and scattering experiments and contributes additional precise spectral data for the N₂ molecule.