Molecular emission of GeO in laser-induced plasma

The molecular emission of germanium monoxide (GeO) formed in laser-induced plasma (LIP) was observed and investigated for the first time. Molecular emission spectroscopy in LIP represents a promising approach, particularly for isotopic analysis. In this work, GeO molecular emission bands were detected in the UV spectral range between 245 and 335 nm following laser ablation of metallic germanium targets in air. The observed emission bands were assigned to the A¹Π − X¹Σ⁺ electronic transition system and exhibit vibrational structures consistent with earlier spectroscopic studies performed in arc-induced plasmas (AIP). Two approaches were evaluated for isotopic analysis: Laser Ablation Molecular Isotopic Spectrometry (LAMIS), based on spontaneous molecular emission from the cooling plasma, and a combined LIBS–MLIF (Laser-Induced Breakdown Spectroscopy coupled with Molecular Laser-Induced Fluorescence) method. The results show that spontaneous GeO emission detected by LAMIS is relatively weak and characterized by broad spectral features, limiting its ability to resolve isotopic shifts. In contrast, the LIBS–MLIF approach significantly enhances spectral selectivity and signal intensity by resonantly exciting GeO molecules with a delayed, tunable laser. The resulting emission spectra exhibit narrower and more intense transitions, enabling the observation of isotope-dependent splitting in several vibrational bands, particularly the 0–5 transition. The measured isotopic shifts are in good agreement with theoretical predictions based on molecular vibrational constants.