Knowledge Bank

Several vibronic bands in the $S1\pm S0$ fluorescence excitation spectrum of 1-naphthaldehyde $(1NA)$ have been rotationally resolved using the new molecular beam laser spectrometer operating in the ultraviolet.2 Typical linewidths are of order 30-50 MHz, making possible the determination of the band origins, the inertial parameters, and the transition moment orientations to high accuracy. Hartree-Fock calculations on the $S0$ state with a 3-21G basis set also have been perfomed. The experimental results suggest that $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}NA$ has a nonplanar equilibrium geometry in its ground electronic state, with a twisted formyl group. Structural changes along this and other coordinates on electronic excitation are revealed by comparisons of the rotational constants of different S1 vibronic levels of 1NA, isotopically labelled 1NA's, and other 1-substituted naphthalenes.2.3