Vibrational wave packet dynamics in NaK: The A state

The NaK 1(b) 3Pi(Omega=0) state hyperfine structure and the 1(b) 3Pi(Omega=0) approximately 2(A) 1Sigma+ spin-orbit interaction

We have measured the hyperfine structure of mutually perturbing rovibrational levels of the 1(b) 3Pi0 and 2(A) 1Sigma+ states of the NaK molecule, using the perturbation-facilitated optical-optical double resonance method with copropagating lasers. The unperturbed 1(b) 3Pi0 levels are split into four hyperfine components by the Fermi contact interaction bFIS. Mixing between the 1(b) 3Pi0 and 2(A) 1Sigma+ levels imparts hyperfine structure to the nominally singlet component of the perturbed levels and reduces the hyperfine splitting of the nominally triplet component. Theoretical analysis relates these observations to the hyperfine splitting that each 1(b) 3Pi0 level would have if it were not perturbed by a 2(A) 1Sigma+ level. Using this analysis, we demonstrate that significant hyperfine splitting arises because the 1(b) 3Pi0 state cannot be described as pure Hund's case (a). We determine bF for the 1(b) 3Pi0 levels and also a more accurate value for the magnitude of the singlet-triplet spin-orbit coupling HSO=[1(b) 3Pi0(vb,J)(H(SO))2(A) 1Sigma+(vA,J). Using the known spectroscopic constants of the 1(b) 3Pi state, we obtain bF=0.009 89+/-0.000 27 cm(-1). The values of (H(SO)) are found to be between 2 and 3 cm(-1), depending on vb, vA, and J. Dividing (H(SO)) by calculated vibrational overlap integrals, and taking account of the 1(b) 3Pi(Omega) rotational mixing, we can determine the magnitude of the electronic part H(el) of H(SO). Our results yield (H(el))=(16.33+/-0.15) cm(-1), consistent with our previous determinations using different techniques.

Photodissociation of bromobenzene, dibromobenzene, and 1,3,5-tribromobenzene

Quantum chemical calculations have been performed on the ground state and several low-lying excited states of bromobenzene, ortho-, meta-, and para-dibromobenzene, and 1,3,5-tribromobenzene using high-level ab initio and hybrid density-functional methods. Experimental observations of ultrafast predissociation in these molecules are clarified from extensive theoretical information about all low-energy potential-energy curves together with symmetry arguments. The intriguing observation that o- and m-dibromobenzene have two ultrafast predissociation channels while bromobenzene, p-dibromobenzene, and 1,3,5-tribromobenzene only have one such channel is explained from the calculated potential-energy curves. These show that the lowering of point-group symmetry from C2v to Cs along the main photodissociation reaction coordinate, which only occurs in o- and m-dibromobenzene, opens up a new predissociation channel. Dynamical quantum simulations based on the calculated potential-energy curves are used to estimate the coupling strength at the intersystem crossing point in bromobenzene.

Potential Energies, Permanent and Transition Dipole Moments for Numerous Electronic Excited States of NaK

Recent experimental works have been devoted to the spectroscopy of highly excited states of NaK, confirming the accuracy of our previous calculations [S. Magnier and Ph. Millié, Phys. Rev. A: Gen. Phys. 54, 204 (1996)] of spectroscopic constants and potential curves. Among them, [E. Laub, I. Mazsa, S. C. Webb, J. La Civita, I. Prodan, Z. J. Zabbour, R. K. Namiotka, and J. Huennekens, J. Mol. Spectrosc. 193, 376 (1999)] have deduced from their measurements the variation of the transition dipole moment with the interatomic distance for the transition X(1)Sigma+ --> (3)(1)Pi. They have shown that a large discrepancy was observed with the previous ab initio calculations currently used as a guide for spectroscopic experiments. Upon request of several experimentalists, we have computed again potential curves for electronic states correlated up to Na(4p) + K(4s) as well as relevant permanent and transition dipole moments. We present extensive predictions for the electronic structure of NaK (potential energies, dipole moments) for which numerical data have been listed in a data base available as supplementary data. Copyright 2000 Academic Press.