Electric quadrupole moments in the CCCBDB by National Institute of Standards and Technology

Experimental molecular quadrupole table: cccbdb.nist.gov/quadlistx.asp

Institutional CCCBDB tutorial, especially the Primitive? Traceless? convention discussion, and experimental benzene entry. No publication date asserted. Its quadrupole convention differs by a factor of two from the Q tensor used in this wiki; no numerical value is transferred between those conventions.