Abstract
Molecular absorption of infrared radiation is generally due to rovibrational electric-dipole transitions. Electric-quadrupole transitions may still occur, but they are typically a million times weaker than electric-dipole transitions, rendering their observation extremely challenging. In polyatomic or polar diatomic molecules, rovibrational quadrupole transitions have never been observed. Here, we report the direct detection of quadrupole transitions in water vapor. The detected quadrupole lines have intensity largely above the standard dipole intensity cutoff of spectroscopic databases and thus are important for accurate atmospheric and astronomical remote sensing.
- Received 8 January 2020
- Accepted 16 March 2020
DOI:https://doi.org/10.1103/PhysRevResearch.2.023091
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Published by the American Physical Society