Knowledge Bank

Molecular quantum beats are observed in the isotropic fluorescence decay following laser excitation of individual rotational states of $C2N2$ {via} the vibronically allowed $401A~(\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma u\mathrm{<mrow\; data-mjx-texclass="ORD">-</mrow>})\leftarrow X~(\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma g\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>})$ transition near 219 nm. Strong quantum beats occur with selective excitation, by both P and R branch transitions, of over a dozen rotational states. Observations of hyperfine quantum beats following excitation of the $N\prime =12$ rotational level yield estimates of spin-orbit coupling matrix elements, Born-Oppenheimer state separations, and magnetic and quadrupolar hyperfine coupling constants. Observations of Zeeman splitting establish that the three hyperfine levels of $N\prime =12$ are coupled to those of a single triplet state.