Abstract
Microwave transitions between the ortho and para states of the 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 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 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.
- Received 9 August 2017
DOI:https://doi.org/10.1103/PhysRevLett.119.173401
© 2017 American Physical Society
Physics Subject Headings (PhySH)
Synopsis
Detection of Ortho-Para Transition in Molecules
Published 25 October 2017
Microwave emission from a simple molecule reveals a highly forbidden transition between two nuclear spin states.
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