Kanamori Hideto, Dehghani Zeinab T, Mizoguchi Asao, Endo Yasuki
Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, Japan.
Department of Applied Chemistry, National Chiao, Tung University, Hsinchu 30010, Taiwan.
Phys Rev Lett. 2017 Oct 27;119(17):173401. doi: 10.1103/PhysRevLett.119.173401. Epub 2017 Oct 25.
Microwave transitions between the ortho and para states of the S_{2}Cl_{2} 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 S_{2}Cl_{2} 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 ortho-para 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.
