Laser-induced fluorescence measurements with an experimental accuracy of 0.002 cm 01 have been performed on the 360-nm band system of NiCl 2 , using a free jet expansion and a heated nozzle. About 80 bands, involving the three main isotopomers, 58 Ni 35 Cl 2 , 58 Ni 35 Cl 37 Cl, and 60 Ni 35 Cl 2 , were analyzed at a rotational temperature of Γ10 K. Assignments of these bands led to the determination of rotational constants for NiCl 2 in many of the states which participate in the observed transitions. The values of the lower state rotational constants prove that the transitions arise from the same electronic ground state as that previously identified in the band system at 460 nm. The values of the upper state rotational constants vary significantly from band to band; in addition, several bands are perturbed, some of them severely. This suggests that several different electronic states are accessible in the 360-nm system and that many of them interact with each other. α§ 1997 Academic Press
CONTENTS
and Gruen (4); both sets of authors were able to identify some weaker bands at longer wavelengths. However, in all 1. Introduction.
these studies, the ultraviolet system was no more than a 2. Experimental Details. single broad feature, completely without structure. The elec-3. Experimental Results. tronic spectrum of NiCl 2 has also been studied with the 3.1. General Description of the 360-nm Band System. sample isolated in an argon matrix, both in absorption (5, 3.2. The A Band Systems. 3.3. The C Band Systems. 6) and in emission with dispersed fluorescence (7, 8). In 3.4. The E Band Systems. contrast to the gas-phase work, quite extensive vibrational 3.5. Other Band Systems. structure was seen in these studies. Similar observations have 3.6. Identification of Isotopomers and Vibrational Progressions. been made more recently in a neon matrix (9). The infrared 3.7. Isotopomer Shifts. spectrum of NiCl 2 has also been recorded, both in the gas 4. Discussion. 4.1. The Nature of the Transitions.
phase (10, 11) and in a matrix (5, 12, 13). These studies 4.2. The Number of Excited States. have identified two vibrational wavenumbers, one at about 4.3. Isotopic Structure. 515 cm 01 assigned as the antisymmetric stretching vibration 4.4. Vibrational Intervals in the Upper Electronic States.
(n 3 ) and the other at 85 cm 01 (13) which is the bending 4.5. Perturbations.
vibration.