The rotational spectrum and hyperfine structure of the methylene radical CH2 studied by far-infrared laser magnetic resonance spectroscopy

Abstract

Thirteen pure rotational transitions of CH₂ in its X̃ ³B₁ ground vibronic state have been measured and assigned using the technique of far‐infrared laser magnetic resonance (LMR) spectroscopy. The energy levels thus determined led to the prediction and subsequent detection by microwave spectroscopy of a further rotational transition 4₀₄–3₁₃, at lower frequency (∼70 GHz). The analysis of these observations yields precise rotational constants as well as spin–spin, spin‐rotation, and hyperfine interaction parameters for gas phase CH₂. Its rotational spectrum may enable interstellar CH₂ to be detected by radio astronomy. Two rotaional transitions within the v₁=1 excited vibrational state have also been identified in the LMR spectrum. Future observations of vibrationally excited CH₂ may afford a means of determining the singlet–triplet splitting in methylene, and studies of CD₂ and CHD will result in improved structural determinations.