Theoretical Calculation of the Low Laying Electronic States of the Molecular Ion RbH + M. KOREK, 1 S. HAMMOUD, 1 T. HARB 2 1 Physics Department, Faculty of Science, Beirut Arab University, P.O. Box 11-5020 Riad, El Solh, Beirut 1107 2809, Lebanon 2 Physics Department, Faculty of Science, Lebanese International University, Mouseitbeh, Beirut, Lebanon Received 30 July 2008; accepted 10 November 2008 Published online 6 July 2009 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/qua.22001 ABSTRACT: Using an ab initio method, the potential energy has been calculated for the 29 lowest molecular states of symmetries 2  + , 2 , 2  for the molecular ion RbH + . The calculation is based on nonempirical pseudopotentials and parameterized -dependent polarization potentials. Gaussian basis sets have been used for both atoms. The spectroscopic constants for 18 electronic sates have been calculated by fitting the calculated energy values to a polynomial in terms of the internuclear distance R. Through the canonical functions approach the eigenvalue E v , the abscissas of the corresponding turning points (R min and R max ) and the rotational constants B v have been calculated up to 24 vibrational levels for the considered bound states. The comparison of the present results with those available in literature shows a very good agreement. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem 110: 787–797, 2010 Key words: molecular ion RbH + ; theoretical calculation; ab initio calculation; vibration rotation calculation; spectroscopic constants Introduction B eginning in the late 1980s, methods to use laser light to cool and confine atoms at un- precedented temperatures have made a dramatic impact on atomic physics. Laser cooled atoms are now used for a wide variety of studies, a few ex- amples being Bose-Einstein condensation, atomic clocks, ultrasensitive isotope detection, ultracold collisions, and quantum information processing. Collisions of atoms at ultracold temperature have received considerable attention because of their im- portance in cooling and trapping of atoms [1, 2] and molecules [3, 4] and their role in high-precision spectroscopy [5, 6]. Collisions of ions and atoms involve higher-order partial waves because of the long-range attractive polarization forces and be- Correspondence to: M. Korek; e-mail: fkorek@yahoo.com International Journal of Quantum Chemistry, Vol 110, 787–797 (2010) © 2009 Wiley Periodicals, Inc.