Knowledge Bank

Several Doppler-free spectroscopic technique were applied to measure the rotational resolved high-resolution absorption and excitation spectra of the $S1$ $1B1u\leftarrow S0$ $1Ag$ electronic transition. Sub-Doppler excitation spectra and the Zeeman effects of the 0-0 }, {\bf 215}, 155 (2002).} and several vibronic bands up to the excess energy around 2410 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ were measured by crossing a laser beam perpendicular to a collimated molecular beam, and the Doppler-free absorption spectra of the bands of excess energy 435 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ }, {\bf 119}, 3691 (2003).} and 1423 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ were also measured by Doppler-free laser polarization labeling spectroscopy at room temperature. The molecular constants of the observed several vibrational states of the $S1$ $1B1u(v\prime )$ and $S0$ $1Ag(v=0)$ state were determined. The local energy shifts were found in the bands higher than 1423 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ band, and identified as originating from the Colliolis interaction with other vibrational levels. The Zeeman splittings were found for all observed bands. The $J,K$-dependences of the observed splittings were studied. As a result, the observed Zeeman effects could be explained to be originating from the magnetic moment of the $S1$ $1B1u$ state induced by mixing with $S2$ $1B3u$ state by $J$-$L$ coupling. }, {\bf 122}, 144303 (2005).}