宇宙電波観測を用いた, 暗黒星雲コアにおける環状C3H2のオルト・パラ比と化学進化の相関に関する研究

Ortho-to-para nuclear spin ratio of cyclopropenylidene (c-C3H2) in TMC-1 cores was investigated using the 45 m radio telescope at Nobeyama Radio Observatory. We have observed four ortho lines (JKaKc=212-101, 312-303, 321-312, and 330-321) and four para lines (J KaKc=202-111, 211-202, 220-211, and 322-313) of c-C3H2 in six cores in TMC-1. A statistical equilibrium analysis of the oserved intensities revealed clear correlation between the ortho-to-para ratio of c-C3H2 and chemical evolution of the molecular cloud; the ortho-to-para ratio in younger cores is less than 2, while that in older cores is close to the statistical ratio of 3. A simple chemical model calculation indicates that the correlation is ascribed to the conservation of nuclear spin angular moment in chemical reactions relevant to the production, destruction, and re-production of c-C3H2.