Detection of Microwave Transitions between Ortho and Para States in a Free Isolated Molecule

Hideto Kanamori*, Zeinab. T. Dehghani, Asao Mizoguchi, Yasuki Endo

*Corresponding author for this work

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Microwave transitions between the ortho and para states of the S2Cl2 molecule in a free isolated condition are observed for the first time. In the theoretical treatment, we derive eigenfunctions of an effective Hamiltonian including the ortho-para interaction to calculate the intensities and frequencies of forbidden ortho-para transitions in the cm-wave region and pick up some promising candidates for the spectroscopic detection. In the experiment, transitions of the S2Cl2 molecule under a supersonic jet condition are observed with a Fourier transform microwave spectrometer. Seven hyperfine resolved rotational transitions including the lowest rotational level are detected as the ortho-para transitions at the predicted frequencies within the experimental errors. The observed intensities are about 10(-3) times the allowed transitions, which are consistent with the predictions based on the intensity-borrowing model. This result suggests that the orthopara conversion of this molecule occurs in a few thousand years through spontaneous emission even in a circumstance where molecular collisions occur rarely like in interstellar space.

Original languageEnglish
Article number173401
Number of pages5
JournalPhysical Review Letters
Issue number17
StatePublished - 25 Oct 2017



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