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# Calibration-quality adiabatic potential energy surfaces for H-3(+) and its isotopologues

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Gorlaeus Laboratories, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
(Impact Factor: 2.95). 05/2012; 136(18):184303. DOI: 10.1063/1.4711756
Source: PubMed

ABSTRACT

Calibration-quality ab initio adiabatic potential energy surfaces (PES) have been determined for all isotopologues of the molecular ion H(3)(+). The underlying Born-Oppenheimer electronic structure computations used optimized explicitly correlated shifted Gaussian functions. The surfaces include diagonal Born-Oppenheimer corrections computed from the accurate electronic wave functions. A fit to the 41,655 ab initio points is presented which gives a standard deviation better than 0.1 cm(-1) when restricted to the points up to 6000 cm(-1) above the first dissociation asymptote. Nuclear motion calculations utilizing this PES, called GLH3P, and an exact kinetic energy operator given in orthogonal internal coordinates are presented. The ro-vibrational transition frequencies for H(3)(+), H(2)D(+), and HD(2)(+) are compared with high resolution measurements. The most sophisticated and complete procedure employed to compute ro-vibrational energy levels, which makes explicit allowance for the inclusion of non-adiabatic effects, reproduces all the known ro-vibrational levels of the H(3)(+) isotopologues considered to better than 0.2 cm(-1). This represents a significant (order-of-magnitude) improvement compared to previous studies of transitions in the visible. Careful treatment of linear geometries is important for high frequency transitions and leads to new assignments for some of the previously observed lines. Prospects for further investigations of non-adiabatic effects in the H(3)(+) isotopologues are discussed. In short, the paper presents (a) an extremely accurate global potential energy surface of H(3)(+) resulting from high accuracy ab initio computations and global fit, (b) very accurate nuclear motion calculations of all available experimental line data up to 16,000 cm(-1), and (c) results suggest that we can predict accurately the lines of H(3)(+) towards dissociation and thus facilitate their experimental observation.

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Available from: Attila Csaszar, Mar 11, 2014
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ABSTRACT: For high-precision calculations of rovibrational states of light molecules, it is essential to include non-adiabatic corrections. In the absence of crossings of potential energy surfaces, they can be incorporated in a single surface picture through coordinate-dependent vibrational and rotational reduced masses. We present a compact method for their evaluation and relate in particular the vibrational mass to a well defined nuclear core mass derived from a Mulliken analysis of the electronic density. For the rotational mass we propose a simple, but very effective parametrization. The use of these masses in the nuclear Schrödinger equation yields numerical data for the corrections of a much higher quality than can be obtained with optimized constant masses, typically better than 0.1 cm(-1). We demonstrate the method for H(2), H(2) (+), and singly deuterated isotopologues. Isotopic asymmetry does not present any particular difficulty. Generalization to polyatomic molecules is straightforward.
The Journal of Chemical Physics 10/2012; 137(16):164316. DOI:10.1063/1.4762442 · 2.95 Impact Factor
• ##### Article: Vibrating H-3(+) in a Uniform Magnetic Field
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ABSTRACT: Potential energy surfaces are obtained for singlet $\rm H_3^+$ in magnetic fields of up to 2350 T. The magnetic interaction was treated by first order perturbation theory and the interaction terms computed {\em ab initio}. They were then fitted to a functional form and added to a recent, highly accurate adiabatic potential energy surface. In its most stable orientation, the molecule is arranged such that the magnetic field vector is in the molecular plane. The most stable configuration is no longer $D_{3h}$ as in the field-free case, but $C_{2v}$, though the stabilization energy is extremely small, of the order of 0.01 $\rm cm^{-1}$ for a 2350 T field. Finally, we have calculated, for a range of magnetic field strengths and orientations, all the vibrational eigenvalues which are below the barrier to linearity in the field-free case.
The Journal of Physical Chemistry A 03/2013; 117(39). DOI:10.1021/jp312856s · 2.69 Impact Factor
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##### Article: Using a Nondirect Product Basis to Compute J>0 Rovibrational States of H3(+)
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ABSTRACT: We have used a Lanczos algorithm with a nondirect product basis to compute energy levels of \hhh with $J$ values as large as 46. Energy levels computed on the potential surface of M.~Pavanello, \ea (\JCP {136}{184303}{2012}) agree well with previous calculations for low $J$ values.
The Journal of Physical Chemistry A 03/2013; 117(39). DOI:10.1021/jp312027s · 2.69 Impact Factor