Doppler-free laser polarization and optical-optical double resonance polarization labeling spectroscopies of a large molecule:: Naphthalene

Doppler-free laser polarization (DFLP) spectroscopy is successfully applied to a large polyatomic molecule, naphthalene. Rotationally resolved spectra of the 33(b(2g))(0)(1) vibronic band of the A B-1(1u)<--X (1)A(g) electronic transition of gas phase naphthalene at room temperature have been measured with the technique of DFLP spectroscopy. The typical width of the observed spectral lines was 15 MHz, and the absolute wave numbers were measured with an accuracy of better than +/-0.0002 cm(-1). In order to assign the dense and complicated parts of the spectra, the technique of Doppler-free optical-optical double resonance polarization labeling spectroscopy was used. Both V-type and Lambda-type double resonances were observed, and these signals were found to be very useful for the unambiguous assignment of the complicated lines of DFLP spectrum. Three rotational constants A, B, and C, three symmetric-top quartic centrifugal distortion constants Delta(J), Delta(JK), and Delta(K), and two asymmetric-top distortion constants delta(J) and delta(K) were determined by a least-squares fitting of 4632 spectral lines in the range J=4-154 and K-a=0-40 with a standard deviation of 0.0002 cm(-1). No appreciable perturbation was observed. (C) 2003 American Institute of Physics.