Publications (7)22.5 Total impact

Article: Communication: Visible line intensities of the triatomic hydrogen ion from experiment and theory
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ABSTRACT: The visible spectrum of H3+ is studied using highsensitivity action spectroscopy in a cryogenic radiofrequency multipole trap. Advances are made to measure the weak rovibrational transitions from the lowest rotational states of H3+ up to high excitation energies providing visible line intensities and, after normalisation to an infrared calibration line, the corresponding Einstein $B$ coefficients. {\it Ab initio} predictions for the Einstein $B$ coefficients are obtained from a highly precise dipole moment surface of H3+ and found to be in excellent agreement, even in the region where states have been classified as chaotic.  [Show abstract] [Hide abstract]
ABSTRACT: This is the third of a series of articles reporting critically evaluated rotational–vibrational line positions, transition intensities, and energy levels, with associated critically reviewed labels and uncertainties, for all the main isotopologues of water. This paper presents experimental line positions, experimentalquality energy levels, and validated labels for rotational–vibrational transitions of the most abundant isotopologue of water, H216O. The latest version of the MARVEL (Measured Active Rotational–Vibrational Energy Levels) lineinversion procedure is used to determine the rovibrational energy levels of the electronic ground state of H216O from experimentally measured lines, together with their selfconsistent uncertainties, for the spectral region up to the first dissociation limit. The spectroscopic network of H216O containstwo components, an ortho (o) and a para (p) one. For oH216O and pH216O, experimentally measured, assigned, and labeled transitions were analyzed from more than 100 sources. The measured lines come from onephoton spectra recorded at room temperature in absorption, from hot samples with temperatures up to 3000 K recorded in emission, and from multiresonance excitation spectra which sample levels up to dissociation. The total number of transitions considered is 184 667 of which 182 156 are validated: 68 027 between para states and 114 129 ortho ones. These transitions give rise to 18 486 validated energy levels, of which 10 446 and 8040 belong to oH216O and pH216O, respectively. The energy levels, including their labeling with approximate normalmode and rigidrotor quantum numbers, have been checked against ones determined from accurate variational nuclear motion computations employing exact kinetic energy operators as well as against previous compilations of energy levels. The extensive list of MARVEL lines and levels obtained are deposited in the supplementary data of this paper, as well as in a distributed information system applied to water, W@DIS, where they can easily be retrieved.  [Show abstract] [Hide abstract]
ABSTRACT: The molecular ion is the simplest polyatomic and polyelectronic molecular system, and its spectrum constitutes an important benchmark for which precise answers can be obtained ab initio from the equations of quantum mechanics. Significant progress in the computation of the rovibrational spectrum of is discussed. A new, global potential energy surface (PES) based on ab initio points computed with an average accuracy of 0.01 cm(1) relative to the nonrelativistic limit has recently been constructed. An analytical representation of these points is provided, exhibiting a standard deviation of 0.097 cm(1). Problems with earlier fits are discussed. The new PES is used for the computation of transition frequencies. Recently measured lines at visible wavelengths combined with previously determined infrared rovibrational data show that an accuracy of the order of 0.1 cm(1) is achieved by these computations. In order to achieve this degree of accuracy, relativistic, adiabatic and nonadiabatic effects must be properly accounted for. The accuracy of these calculations facilitates the reassignment of some measured lines, further reducing the standard deviation between experiment and theory.  [Show abstract] [Hide abstract]
ABSTRACT: Given the large energy required for its electronic excitation, the most important properties of the water molecule are governed by its ground potential energy surface (PES). Novel experiments are now able to probe this surface over a very extended energy range, requiring new theoretical procedures for their interpretation. As part of this study, a new, accurate, global spectroscopicquality PES and a new, accurate, global dipole moment surface are developed. They are used for the computation of the highresolution spectrum of water up to the first dissociation limit and beyond as well as for the determination of Stark coefficients for highlying states. The water PES has been determined by combined ab initio and semiempirical studies. As a first step, a very accurate, global, ab initio PES was determined using the allelectron, internally contracted multireference configuration interaction technique together with a large Gaussian basis set. Scalar relativistic energy corrections are also determined in order to move the energy determinations close to the relativistic complete basis set full configuration interaction limit. The electronic energies were computed for a set of about 2500 geometries, covering carefully selected configurations from equilibrium up to dissociation. Nuclear motion computations using this PES reproduce the observed energy levels up to 39 000 cm(1) with an accuracy of better than 10 cm(1). Line positions and widths of resonant states above dissociation show an agreement with experiment of about 50 cm(1). An improved semiempirical PES is produced by fitting the ab initio PES to accurate experimental data, resulting in greatly improved accuracy, with a maximum deviation of about 1 cm(1) for all vibrational band origins. Theoretical results based on this semiempirical surface are compared with experimental data for energies starting at 27 000 cm(1), going all the way up to dissociation at about 41 000 cm(1) and a few hundred wavenumbers beyond it.  [Show abstract] [Hide abstract]
ABSTRACT: Calibrationquality ab initio adiabatic potential energy surfaces (PES) have been determined for all isotopologues of the molecular ion H(3)(+). The underlying BornOppenheimer electronic structure computations used optimized explicitly correlated shifted Gaussian functions. The surfaces include diagonal BornOppenheimer 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 rovibrational 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 rovibrational energy levels, which makes explicit allowance for the inclusion of nonadiabatic effects, reproduces all the known rovibrational levels of the H(3)(+) isotopologues considered to better than 0.2 cm(1). This represents a significant (orderofmagnitude) 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 nonadiabatic 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.  [Show abstract] [Hide abstract]
ABSTRACT: Firstprinciples computations and experimental measurements of transition energies are carried out for vibrational overtone lines of the triatomic hydrogen ion H(3)(+) corresponding to floppy vibrations high above the barrier to linearity. Action spectroscopy is improved to detect extremely weak visiblelight spectral lines on cold trapped H(3)(+) ions. A highly accurate potential surface is obtained from variational calculations using explicitly correlated Gaussian wave function expansions. After nonadiabatic corrections, the floppy H(3)(+) vibrational spectrum is reproduced at the 0.1 cm(1) level up to 16600 cm(1).  [Show abstract] [Hide abstract]
ABSTRACT: The molecular ion ${\rm{H}}_{\rm{3}}^{\rm{ + }}$ is the simplest polyatomic and polyelectronic molecular system, and its spectrum constitutes an important benchmark for which precise answers can be obtained ab initio from the equations of quantum mechanics. Significant progress in the computation of the rovibrational spectrum of ${\rm{H}}_{\rm{3}}^{\rm{ + }}$ is discussed. A new, global potential energy surface (PES) based on ab initio points computed with an average accuracy of 0.01 cm⁻¹ relative to the nonrelativistic limit has recently been constructed. An analytical representation of these points is provided, exhibiting a standard deviation of 0.097 cm⁻¹. Problems with earlier fits are discussed. The new PES is used for the computation of transition frequencies. Recently measured lines at visible wavelengths combined with previously determined infrared rovibrational data show that an accuracy of the order of 0.1 cm⁻¹ is achieved by these computations. In order to achieve this degree of accuracy, relativistic, adiabatic and nonadiabatic effects must be properly accounted for. The accuracy of these calculations facilitates the reassignment of some measured lines, further reducing the standard deviation between experiment and theory.
Publication Stats
156  Citations  
22.50  Total Impact Points  
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Institutions

20122014

Russian Academy of Sciences
 Institute of Applied Physics
Moskva, Moscow, Russia
