225 research outputs found
On the use of reduced-density matrices for the semi-automatic assignment of vibrational states
The use of one- and two-mode reduced-density matrices (RDM), and , respectively, and in particular the use of their diagonal elements, and , is suggested for the assignment of normal-mode-like quantum numbers to variationally computed vibrational wave functions of semirigid molecules when the computation is based on a nuclear-motion Hamiltonian expressed in curvilinear internal coordinates . The use of RDMs for the semi-automatic assignment of vibrational states is tested on the HO molecule, whereby about the first 250 states, in the energy range of 0-25,000cm(-1), are assigned. The proposed semi-automatic assignment procedure takes advantage of the fact that (a) for semirigid molecules it is often possible to define internal coordinates which mimick normal coordinates defined by the harmonic counterparts of the anharmonic vibrations, (b) overlaps between already assigned and yet unassigned RDMs provide outstanding and often unambiguous suggestions for the quantum numbers, and (c) an energy-decomposition scheme helps to decide among possible assignment possibilities suggested by the computed density overlaps. [GRAPHICS]
High accuracy calculations of the rotation-vibration spectrum of H
Calculation of the rotation-vibration spectrum of H3+, as well as of its
deuterated isotopologues, with near-spectroscopic accuracy requires the
development of sophisticated theoretical models, methods, and codes. The
present paper reviews the state-of-the-art in these fields. Computation of
rovibrational states on a given potential energy surface (PES) has now become
standard for triatomic molecules, at least up to intermediate energies, due to
developments achieved by the present authors and others. However, highly
accurate Born--Oppenheimer energies leading to highly accurate PESs are not
accessible even for this two-electron system using conventional electronic
structure procedures e.g., configuration-interaction or coupled-cluster
techniques with extrapolation to the complete basis set limit). For this
purpose highly specialized techniques must be used, e.g., those employing
explicitly correlated Gaussians and nonlinear parameter optimizations. It has
also become evident that a very dense grid of \ai\ points is required to obtain
reliable representations of the computed points extending from the minimum to
the asymptotic limits. Furthermore, adiabatic, relativistic, and QED correction
terms need to be considered to achieve near-spectroscopic accuracy during
calculation of the rotation-vibration spectrum of H3+. The remaining and most
intractable problem is then the treatment of the effects of non-adiabatic
coupling on the rovibrational energies, which, in the worst cases, may lead to
corrections on the order of several \cm. A promising way of handling this
difficulty is the further development of effective, motion- or even
coordinate-dependent, masses and mass surfaces. Finally, the unresolved
challenge of how to describe and elucidate the experimental pre-dissociation
spectra of H and its isotopologues is discussed.Comment: Topical review to be published in J Phys B: At Mol Opt Phy
From continental platform towards rifting of the Tisza Unit in the Late Triassic to Early Cretaceous
The Upper Triassic-Lower Cretaceous successions of the Transdanubian part of the Mecsek and Villany-Bihor Zones of the Tisza Unit have been studied from the lithological, lithostratigraphical, sedimentological, microfossil and microfacies points of view in order to correlate and interpret the significant differences between them and to draw a conclusion about their geological and paleogeographical history. After an overview of the paleogeographical reconstructions of the broader area, the succession of the Mecsek and Villany-Bihor Zones and the debated Mariakemend-Bar Range are introduced. Until the end of the Middle Triassic the study area acted as an entity. The first fundamental difference between the two zones can be recognized in the Late Triassic when marine carbonates were replaced by thick fluvial siliciclastics in the Mecsek Zone, while it is represented only by small, local lenses with a few and thin dolostone intercalations in the Villany Zone. The Mecsek Zone is bordered southward by one of the large listric faults to the north of which very thick siliciclastics developed in the Early to Middle Jurassic, whereas it is highly lacunose in the larger western part of the Villany-Bihor Zone. The break at the base is subaerial, higher in the succession it is shallow submarine. The sediment is silty, occasionally sandy crinoidal limestone of late Early Jurassic or even Middle Jurassic in age. The Upper Jurassic in the Mecsek Zone is composed of deep-water cherty limestone while in the Villany Zone it became a thick, shallowing pelagic limestone with reworked patch reef fragments. It is clear evidence that the Mecsek Zone had a thinned continental crust thanks to the nearby rift zone while in the Villany Zone the crust remained thick. The actualized version of the Plasienka's paleogeographical model (Plasienka 2000) is introduced
Experimental energy levels and partition function of the C molecule
The carbon dimer, the C molecule, is ubiquitous in astronomical
environments. Experimental-quality rovibronic energy levels are reported for
C, based on rovibronic transitions measured for and among its
singlet, triplet, and quintet electronic states, reported in 42 publications.
The determination utilizes the Measured Active Rotational-Vibrational Energy
Levels (MARVEL) technique. The 23,343 transitions measured experimentally and
validated within this study determine 5,699 rovibronic energy levels, 1,325,
4,309, and 65 levels for the singlet, triplet, and quintet states investigated,
respectively. The MARVEL analysis provides rovibronic energies for six singlet,
six triplet, and two quintet electronic states. For example, the lowest
measurable energy level of the \astate\ state, corresponding to the total
angular momentum quantum number and the spin-multiplet component, is
603.817(5) \cm. This well-determined energy difference should facilitate
observations of singlet--triplet intercombination lines which are thought to
occur in the interstellar medium and comets. The large number of highly
accurate and clearly labeled transitions that can be derived by combining
MARVEL energy levels with computed temperature-dependent intensities should
help a number of astrophysical observations as well as corresponding laboratory
measurements. The experimental rovibronic energy levels, augmented, where
needed, with {\it ab initio} variational ones based on empirically adjusted and
spin-orbit coupled potential energy curves obtained using the \Duo\ code, are
used to obtain a highly accurate partition function, and related thermodynamic
data, for C up to 4,000 K.Comment: ApJ Supplements (in press), 48 page
Uncertainty Estimates for Theoretical Atomic and Molecular Data
Sources of uncertainty are reviewed for calculated atomic and molecular data
that are important for plasma modeling: atomic and molecular structure and
cross sections for electron-atom, electron-molecule, and heavy particle
collisions. We concentrate on model uncertainties due to approximations to the
fundamental many-body quantum mechanical equations and we aim to provide
guidelines to estimate uncertainties as a routine part of computations of data
for structure and scattering.Comment: 65 pages, 18 Figures, 3 Tables. J. Phys. D: Appl. Phys. Final
accepted versio
MARVEL Analysis of the Measured High-Resolution Rovibronic Spectra of 90Zr16O
Zirconium oxide(ZrO) is an important astrophysical molecule that defines the
S-star classification class for cool giant stars. Accurate, empirical
rovibronic energy levels, with associated labels and uncertainties, are
reported for 9 low-lying electronic states of the diatomic 90Zr16O molecule.
These 8088 empirical energy levels are determined using the Marvel (Measured
Active Rotational-Vibrational Energy Levels) algorithm with 23 317 input
assigned transition frequencies, 22 549 of which were validated. A
temperature-dependent partition function is presented alongside updated
spectroscopic constants for the 9 low-lying electronic states
An improved rovibrational linelist of formaldehyde, H212C16O
Published high-resolution rotation-vibration transitions of H212C16O, the principal isotopologue of methanal, are analyzed using the MARVEL (Measured Active Rotation-Vibration Energy Levels) procedure. The literature results are augmented by new, high-accuracy measurements of pure rotational transitions within the ground, ν3, ν4, and ν6 vibrational states. Of the 16 596 non-redundant transitions processed, which come from 43 sources including the present work, 16 403 could be validated, providing 5029 empirical energy levels of H212C16O with statistically well-defined uncertainties. All the empirical rotational-vibrational energy levels determined are used to improve the accuracy of ExoMol's AYTY line list for hot formaldehyde. The complete list of collated experimental transitions, the empirical energy levels determined, as well as the extended and improved line list are provided as Supplementary Material
Recommended isolated-line profile for representing high-resolution spectroscopic transitions (IUPAC Technical Report)
The report of an IUPAC Task Group, formed in 2011 on "Intensities and line
shapes in high-resolution spectra of water isotopologues from experiment and
theory" (Project No. 2011-022-2-100), on line profiles of isolated
high-resolution rotational-vibrational transitions perturbed by neutral
gas-phase molecules is presented. The well-documented inadequacies of the Voigt
profile (VP), used almost universally by databases and radiative-transfer
codes, to represent pressure effects and Doppler broadening in isolated
vibrational-rotational and pure rotational transitions of the water molecule
have resulted in the development of a variety of alternative line-profile
models. These models capture more of the physics of the influence of pressure
on line shapes but, in general, at the price of greater complexity. The Task
Group recommends that the partially Correlated quadratic-Speed-Dependent
Hard-Collision profile should be adopted as the appropriate model for
high-resolution spectroscopy. For simplicity this should be called the
Hartmann--Tran profile (HTP). The HTP is sophisticated enough to capture the
various collisional contributions to the isolated line shape, can be computed
in a straightforward and rapid manner, and reduces to simpler profiles,
including the Voigt profile, under certain simplifying assumptions.Comment: Accepted for publication in Pure and Applied Chemistr
IUPAC Critical Evaluation of the Rotational-Vibrational Spectra of Water Vapor, Part III: Energy Levels and Transition Wavenumbers for H216O
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, experimental-quality 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) line-inversion procedure is used to determine the rovibrational energy levels of the electronic ground state of H216O from experimentally measured lines, together with their self-consistent uncertainties, for the spectral region up to the first dissociation limit. The spectroscopic network of H216O contains two components, an ortho (o) and a para (p) one. For o-H216O and p-H216O, experimentally measured, assigned, and labeled transitions were analyzed from more than 100 sources. The measured lines come from one-photon spectra recorded at room temperature in absorption, from hot samples with temperatures up to 3000K recorded in emission, and from multiresonance excitation spectra which sample levels up to dissociation. The total number of transitions considered is 184667 of which 182156 are validated: 68027 between para states and 114129 ortho ones. These transitions give rise to 18486 validated energy levels, of which 10446 and 8040 belong to o-H216O and p-H216O, respectively. The energy levels, including their labeling with approximate normal-mode and rigid-rotor 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
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