Accurate ab initio potential for the Na+⋯I• complex

Abstract

High-level ab initio calculations employing the multireference configuration interaction and coupled clusters methods with a correlation-consistent sequence of basis sets have been used to obtain accurate potential energy curves for the complex of the sodium cation with the iodine atom. Potential curves for the first two electronic Lambda-S states have very different characters: the potential for the 2pi state has a well depth of approximately 10 kcal/mol, while the 2sigma state is essentially unbound. This difference is rationalized in terms of the anisotropic interaction of the quadrupole moment of the iodine atom with the sodium cation, which is stabilizing in the case of the 2pi state and destabilizing in the case of the 2sigma state. The effects of spin-orbit coupling have been accounted for with both ab initio and semiempirical approaches, which have been found to give practically the same results. Inclusion of spin-orbit interactions does not affect the X(omega = 32) ground state, which retains its 2pi character, but it results in two omega = 12 spin-orbit states, with mixed 2sigma and 2pi characters and binding energies roughly half of that of the ground spin-orbit state. Complete basis set (CBS) extrapolations of potential curves, binding energies, and equilibrium geometries were also performed, and used to calculate a number of rovibronic parameters for the Na+...I* complex and to parameterize model potentials. The final CBS-extrapolated and zero-point vibrational energy-corrected binding energy is 10.2 kcal/mol. Applications of the present results for simulations of NaI photodissociation femtosecond spectroscopy are discussed.

Potential energy surfaces and nonadiabatic transitions in the asymptotic regions of ICN photodissociation to study the interference effects in the F1 and F2 spin‐rotation levels of the CN products

“…The experimental values of μ CN and Q are 0.5738 a.u . and 2.536 a.u., respectively. Therefore μ CN Q > 0 and the eigenstates | v ± 〉 at θ = 0 are given as …”

“…The electrostatic dipole–quadrupole interaction has a time‐reversal symmetry, and the doubly degeneracy is a consequence of Kramers degeneracy for the odd number of electrons on I atom. We obtained the model PECs by substituting the experimental values for μ CN and Q in eq. and compare their functional behaviors with our PECs calculated by COSOCI method in Figures a and 5b.…”

Photoexcitation and Charge-Transfer-to-Solvent Relaxation Dynamics of the I–(CH3CN) Complex

“…The SO mixing of the 1 1 E and 2 1 A 1 states of the excited complex gives rise to three SO states, labeled I, II, and III (X is used for the ground state of the I − (CH 3 CN) complex, which is essentially the 1 1 A 1 state); the first two states correlate with the 2 P 3/2 limit of the free iodine atom, whereas the third one correlates with the 2 P 1/2 limit. 81,82 For a complex with cylindrical symmetry, such as Na + We now turn our attention to more quantitative aspects of the photoionization and photoexcitation of I − (CH 3 CN). As we have demonstrated previously, 86 ab initio (MP2) calculations predict binding energies for the binary halide−acetonitrile clusters in excellent agreement with experimental data.…”

“…The potential energy curves for the 1 2 E and 1 2 A 1 states of I • (CH 3 CN) have substantially different well depths due to the nonspherical distribution of the electron density of the iodine atom, giving rise to a nonzero quadrupole moment and relatively large differences in the polarizability along different axes. 82 In the lower 1 2 E state, the interaction between acetonitrile and the iodine atom (located on the methyl group side) is relatively strong, with a potential well of ∼50 meV (∼1.2 kcal/mol) at a C−I distance of ∼4 Å (Figure 3). The well depth for the 1 2 A 1 state is only 23 meV (∼0.5 kcal/ mol), and the potential energy minimum is located at a shorter acetonitrile−iodine distance, with r(C−I) = 3.8 Å.…”

Ab initio study on the ground and low-lying excited states of cesium iodide (CsI)

“…Among these, NaI might be the most thoroughly investigated molecule from both experimental 1-7 and theoretical [8][9][10][11][12][13][14][15][16] points of view. It has been established for diatomic alkali halides that the covalent and ionic potential energy curves ͑PECs͒ cross at an avoided crossing ͑AC͒ point and the covalent and ionic PECs are repulsive and strongly bound, respectively, when the internuclear distance is relatively small.…”