Resonance enhanced two photon ionization study in a pulsed molecular beam identified spin-forbidden transitions of the 2 3Πu(1u)–X 1Σg+(0g+) and 2 3Πu(0u+)–X 1Σg+(0g+) of Rb2. Λ-doubling and interference-induced rotational branch intensity anomalies are observed for 2 3Πu(1u)–X 1Σg+(0g+) transitions. The rotational constant for the 2 3Πu state was determined to be Be=0.018 932 5±0.000 007 4 cm−1 for Rb285, giving Re=4.5796±0.0009 Å. Other molecular parameters for Rb285 are determined as Te=19 784.254±0.009 cm−1, ωe=42.200±0.006 cm−1, ωexe=0.171±0.001 cm−1, and ωeye=−0.001 06±0.000 06 cm−1 for the 2 3Πu(0u+) state and Te=19 785.74±0.01 cm−1, ωe=42.297±0.005 cm−1, ωexe=0.1725±0.0009 cm−1, and ωeye=−0.000 78±0.000 04 cm−1 for 2 3Πu(1u) state. These Re, ωe, and Te values agree well with ab initio calculated values. The spin–orbit coupling constant A and Λ-doubling parameters p and q are determined by simultaneous fitting of the rotational structures of both 2 3Πu(1u)−X 1Σg+ and 2 3Πu(0u+)−X 1Σg+ transitions.

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Motivated by our recent finding that the singlet-triplet bands of selenoformaldehyde involve an upper state with large zero field splittings, we have extended the theory and written a program for predicting and fitting such rotationally resolved spectra. Triplet state matrix elements for a case ͑A͒ basis have been developed, including corrections for centrifugal and spin-centrifugal distortion. The full Hamiltonian matrix has been symmetry adapted, simplifying the problem to four individual matrices of approximately equal size for molecules of orthorhombic symmetry. Diagonalization of these matrices yields triplet state energies that are in agreement with previous treatments using a basis in which the spin splittings are small relative to the rotational intervals. Methods have been developed for sorting the eigenvalues and assigning quantum labels regardless of the magnitude of the spin splittings. The calculation of the relative intensities of the rotational lines within a band has been programmed using transition moment matrix elements from the literature. The selection rules for various upper state symmetries have been developed in a form useful for the analysis of spectra. Band contour predictions of spectra for various coupling cases have been presented.

A vibronically and partially rotationally resolved electronic spectrum of chlorofluorocarbene has been observed using the technique of pyrolysis jet spectroscopy. A vibrational analysis has established the origin of the electronic transition to be at 25 277.8 cm−1. The pattern of isotope effects for the CF35Cl and CF37Cl species was used to confirm the vibrational assignments. The rotational analysis of three bands established that the transition moment is perpendicular to the molecular plane and can be assigned as Ã 1A″–X̃ 1A′. The ground and excited state geometries were derived from the rotational analysis and compared to ab initio predictions. The transition was found to be the direct analog of the 600 nm band system of dichlorocarbene.

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