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By selecting a number of resonant A 21 rotational lines in the optical–optical double resonance multiphoton ionization spectroscopy (OODR‐MPI) of ammonia‐d3, we have obtained rotationally resolved spectra of the ND3 B←A 21←X 00 transitions in the range of 550–730 nm, in which not only were we able to reanalyze rotationally the previously studied bands [J. Opt. Soc. Am. B 7, 1884(1990)], but also to assign rotationally and vibronically some novel spectra pertaining to the ν1, ν3, ν4, and ν3+ν4 excitations. Based on the symmetry assignment and the relationship of the vibronic coupling level energies between the single and dual mode cases, we have found that the Jahn–Teller splitting of the ND3 B state invokes a novel type of the Fermi resonance, the nonadiabatic Fermi resonance. By taking account of this Fermi resonance, the modified vibronic coupling parameters of the ν3 and ν4 modes were calculated to be λ3=0.047 and λ4=0.023, which agrees well with the previous theoretical expectation that the ammon...

The fine structure of the b(1)3Πu state of the lithium dimer was observed for the first time and studied using Doppler‐free polarization spectroscopy. The triplet state was accessed by excitation of the A 1Σ+u(v=2,J=33)∼b(1)3Πu (v=9,N=32,F1,e) spin–orbit perturbed levels. The remaining two fine structure levels were excited by using the Zeeman interaction to mix levels of different J. Two polarization geometries, π pump and σ pump, were used to study separately different groups of MJ levels in magnetic fields up to 3 kG. An irreducible tensor derivation of the fine structure and Zeeman Hamiltonian matrix in Hund’s case (b) symmetrized basis functions was carried out and used to determine the perturbation parameters and the spin–spin and spin–rotation fine structure constants by a fit to the Zeeman splitting pattern. The spin–orbit contribution to the fine structure is too small in the high J states to be found accurately. The electronic spin–orbit coupling perturbation for the interaction between the sing...

The third order nonlinear optical properties of a trimer branched chromophore system and its linear molecule analog are investigated. Two-photon absorption and degenerate four wave mixing measurements were carried out on both systems. An enhancement in the nonlinear optical effect is observed for the branched trimer molecule in comparison to the linear chromophore system. Ultrafast time-resolved measurements were carried out to probe the excited state dynamics in the branched structures. The time-resolved measurements suggest that the two important processes affecting the nonlinear optical properties in the trimer system, charge transfer stabilization and initial electronic delocalization, occur on two different time scales.

Presentation des spectres de rotation magnetique. Observation de la fluorescence de bande large a partir des niveaux perturbes de A 1 Σ u + ∼b 3 Π u . Comparaison de la methode d'analyse de rotation magnetique et d'autres methodes pour la fluorescence

Rotationally resolved 6Li2 2 3Πg→a 3Σ+u fluorescence spectra have been obtained by perturbation facilitated optical–optical double resonance spectroscopy. Principal molecular constants for the a 3Σ+u first excited state of 6Li2 are (2σ uncertainties): Te =8180.9±5.4 cm−1, ωe =73.0±1.4 cm−1, ωexe =3.95±0.14 cm−1, Re =4.13±0.08 A, and De =336.0±5.4 cm−1. Transitions into 0≤v≤6 and N=18, 20, 31, 33 were observed and the total number of bound rotation–vibration levels was computed to be 193 for the a 3Σ+u state of 6Li2.