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

Abstract

Potential energy curves (PECs) for the ground and low-lying excited states of the cesium iodide (CsI) molecule have been calculated using the internally contracted multireference configuration interaction calculation with single and double excitation method with the relativistic pseudopotentials. PECs for seven Lambda-S states, X 1Sigma+, 2 1Sigma+, 3Sigma+, 1Pi, and 3Pi are first calculated and then those for 13 Omega states are obtained by diagonalizing the matrix of the electronic Hamiltonian H(el) plus the effective one-electron spin-orbit (SO) Hamiltonian H(SO). Spectroscopic constants for the calculated ground X 0+-state PEC with the Davidson correction are found to agree well with the experiment. Transition dipole moments (TDMs) between X 0 and the other Omega states are also obtained and the TDM between X 0+ and A 0+ is predicted to be the largest and that between X 0+ and B 0+ is the second largest around the equilibrium internuclear distance. The TDMs between X 0+ and the Omega=1 states are estimated to be nonzero, but they are notably small as compared with those between the 0+ states. Finally, vibrational levels of the X 0+ PEC for the two isotopic analogs, (133)CsI and (135)CsI, are numerically obtained to investigate the isotope effect on the vibrational-level shift. It has been found that the maximized available isotope shift is approximately 30 cm(-1) around nu=136.

Multilevel effect on ultrafast isotope-selective vibrational excitations: Quantum optimal control study

“…It sounds reasonable to think that the multilevel effect benefits from large isotope shifts (i.e., difference in energy of the same vibrational level v between the two isotopic molecules) of higher vibrational levels than the lowest two. As we have predicted [12], the higher the vibrational level, the larger the isotope shift in the energy region well below the dissociation aymptote. We here display again in Fig.…”

“…A mixture of the two isotopic species 133 CsI and 135 CsI is considered and the initial state is set to be the condition that both the isotopic species are in the vibrational ground level (v = 0) and the target state is that 133 CsI is in the v = 0 level while 135 CsI in the vibrational first-excited level (v = 1). We used the PEC and dipole moment for the electronic ground state (X0 + ) of CsI, which we have calculated recently at a high level of quantum-chemical theory [12]. The vibrational eigenstates and energies for the X0 + PECs for 133 CsI and 135 CsI were calculated using the Fourier grid Hamiltonian method [13] with 1024 evenly spaced grid points on the internuclear distance from 3.7795 to 35.0 bohr.…”

Quantum control study of multilevel effect on ultrafast isotope-selective vibrational excitations

“…The number of grid points 1024 is also sufficient because the number of bound states supported in the X0 + PEC is about 630, as calculated in Ref. 27. In Table I are given energies of the lowest 10 vibrational eigenstates for the X0 + PECs of 133 CsI and 135 CsI with respect to the PEC bottom, calculated with the 512 and 1024 grid points.…”

“…2 in Ref. 27, the X0 + PEC almost reaches the dissociation limit in energy when the internuclear distance is ϳ15 Å ͑ϳ28 bohr͒. The grid edge of 35.0 bohr is slightly larger than this critical distance and considered to be appropriate.…”

“…In this work a mixture of the two isotopomers 133 CsI and 135 CsI is considered and the initial state is that both the molecules are in the vibrational ground level ͑v =0͒ and the target state is that 133 CsI is in the v = 0 level while 135 CsI in the vibrational first-excited level ͑v =1͒. We used the PEC and dipole moment for the electronic ground-state ͑X0 + ͒ of CsI, which we 27 have calculated recently using the multireference configuration interaction method with the relativistic pseudopotentials including the spin-orbit interaction. The vibrational eigenstates and energies for the X0 + PECs for 133 CsI and 135 CsI were calculated using the Fourier grid Hamiltonian method 28 with 1024 evenly spaced grid points on the internuclear distance from 3.7795 to 35.0 bohr.…”