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An ab initio adiabatic and diabatic study of the KH molecule is performed for all states below the ionic limit [i.e., K (4s, 4p, 5s, 3d, 5p, 4d, 6s, and 4f)+H(1s)] in 1Σ+ and 3Σ+ symmetries. Adiabatic results are also reported for 1Π, 3Π, 1Δ, and 3Δ symmetries. The ab initio calculations rely on pseudopotential, operatorial core valence correlation, and full valence CI approaches, combined to an efficient diabatization procedure. For the low-lying states, our vibrational level spacings and spectroscopic constants are in very good agreement with the available experimental data. Diabatic potentials and dipoles moments are analyzed, revealing the strong imprint of the ionic state in the 1Σ+ adiabatic states while improving the results. The undulations of the diabatic curves and of the triplet–singlet diabatic energy difference which we found positive, as in Hund’s rule, are related to the Rydberg functions. As for LiH, the vibrational spacing of the A state is bracketed by our results with and without the improvement taking into account the diabatic representation. Experimental suggestions are also given.

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In this article, dynamic couplings for X-A, X-C, and A-C, by using first and second derivatives terms neglected in the Born–Oppenheimer approximation, are calculated. Newly calculated radiative transition probabilities for the A1Σ+→X1Σ+ and C1Σ+→X1Σ+ emission bands of KH are used to calculate the radiative and nonradiative lifetimes of the various vibrational levels (0⩽v⩽35) and (0⩽v⩽55) of A1Σ+ and C1Σ+ states of the diatomic potassium hydride, KH, molecule. For higher vibrational levels, an estimate of the bound-to-free emission probability is also needed and included. Accurate positions, radiative and nonradiative lifetimes of states belonging to the adiabatic A and C states of the KH molecule are estimated. The results come from a Fermi’s Golden Rule treatment in coupling calculation. That confirms the accuracy reached in both approaches and also in the treatment of the diabatic-adiabatic transformation. It involves, in particular, an effective phase choice that is needed to properly estimate nonadiabatic couplings.

The results of the present many-electron configuration interaction calculations on the cation support the previous core-polarization effective potential calculations. The present calculations on the CsLi molecule are complementary to previous theoretical work on this system, including recently observed electronic states that had not been calculated previously. We have used an ab initio approach involving a nonempirical pseudopotential for the Li (1s 2 ) and Cs cores and a core-valence correlation correction. A very good agreement of data from spectroscopic constants for some of the lowest states of the CsLi and CsLi + molecules with those available in recent theoretical works has been obtained. The existence of numerous avoided crossings between electronic states of 2 Σ + and 2 Π symmetries is related to a charge transfer process between the two ionic CsLi + and LiCs + systems.Introduction. The research on ultracold molecules presents a current and great challenge to a spectroscopic study of alkali dimers because of both their importance in the cooling and trapping of atoms [1, 2] and molecules [3][4][5][6] and the role in high-precision spectroscopy [7][8][9]. Ultracold molecules should prove to be useful in spectroscopy and the study of molecular structure, especially in ultrahigh resolution spectroscopy which requires cold and trapped samples. Neutral-atom collisions at ultracold temperatures may be characterized by s-wave scattering lengths. Collisions of ions and atoms involve higher-order partial waves because of the long-range attractive polarization forces and differ due to the charge transfer.Another especially promising area will be the study of collisions between ultracold molecules in a regime where they will behave like waves, which perhaps may give rise to new chemistry [10][11][12]. Cooling and manipulating the cold molecules is likely to open up new branches of research. There are experiments aimed at studying polar molecular systems in order to measure the electron's permanent electric dipole moment (EDM), the lifetime of long-lived energy levels, and the effects of dipole-dipole interactions on the molecular sample properties [13]. Recent advances in precision control of an optical spectrum emitted by a femtosecond laser have made a revolutionary impact on the fields of optical frequency metrology (via self-referenced, ultra-broad bandwidth frequency combs) and ultrafast optical science (via carrier-envelope phase stabilized pulse trains). These advances have, in effect, provided an entirely new class of optical sources available for experimental investigations, which are the femtosecond lasers + cold atoms/molecules. The use of pseudopotentials for Li and Cs cores reduces the number of active electrons to only one valence electron, where a self-consistent field (SCF) calculation produces the exact energy in the basis and the main source of errors corresponds to the basis-set limitations. Furthermore we correct the energy by taking into account the core-core