Doppler-free high resolution laser spectroscopies of the naphthalene molecule

Abstract

In this work, a variety of techniques, namely Doppler-free polarization labeling spectroscopy, Doppler-free two photon absorption spectroscopy, and laser excitation spectroscopy with reduced Doppler width achieved by crossing a laser beam at right angles to a collimated molecular beam, have been employed to generate fully rotationally resolved spectra of the naphthalene molecule. The A 1 B 1 u (v 8=1: b 2 g )← X 1 A g (v=0) transition has been investigated by means of Doppler-free laser polarization spectroscopy. This is the first application of this technique to the study of a large polyatomic molecule, and when complemented with an optical–optical double resonance it is demonstrated to be very effective. The A 1 B 1 u (v 4=1: b 1 u )← X 1 A g (v=0) transition has been recorded by means of two-photon absorption spectroscopy with counter propagating light beams of identical wavelength within an external cavity. Additionally, the effects of an external magnetic field were measured, and the Zeeman splittings were observed to increase with increasing the rotational quantum number J. The Zeeman splittings of the A 1 B 1 u (v 8=1: b 2 g ,J) levels, which lie 1100 cm −1 below the A 1 B 1 u (v 4=1: b 1 u ,J) levels, were measured by means of laser excitation spectroscopy by which a laser beam is crossed with a collimated molecular beam. The magnetic moment of the A 1 B 1 u (v 8=1: b 2 g ,J) level was observed to be smaller than that of the A 1 B 1 u (v 4=1: b 1 u ,J) level.