119 research outputs found
Vibrational states of the triplet electronic state of H3+. The role of non-adiabatic coupling and geometrical phase
Vibrational energies and wave functions of the triplet state of the H3+ ion
have been determined. In the calculations, the ground and first excited triplet
electronic states are included as well as the non-Born-Oppenheimer coupling
between them. A diabatization procedure transforming the two adiabatic ab
initio potential energy surfaces of the triplet-H3+ state into a 2x2 matrix is
employed. The diabatization takes into account the non-Born-Oppenheimer
coupling and the effect of the geometrical phase due to the conical
intersection between the two adiabatic potential surfaces. The results are
compared to the calculation involving only the lowest adiabatic potential
energy surface of the triplet-H3+ ion and neglecting the geometrical phase. The
energy difference between results with and without the non-adiabatic coupling
and the geometrical phase is about a wave number for the lowest vibrational
levels
QED correction for H
A quantum electrodynamics (QED) correction surface for the simplest
polyatomic and polyelectronic system H is computed using an approximate
procedure. This surface is used to calculate the shifts to vibration-rotation
energy levels due to QED; such shifts have a magnitude of up to 0.25 cm
for vibrational levels up to 15~000 cm and are expected to have an
accuracy of about 0.02 cm. Combining the new H QED correction
surface with existing highly accurate Born-Oppenheimer (BO), relativistic and
adiabatic components suggests that deviations of the resulting {\it ab initio}
energy levels from observed ones are largely due to non-adiabatic effects
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
Ro-Vibrational States of Triplet H2D
We present rotational term values for J ≤ 3 of the vibrational states with up to twofold excitation of H2D+ in the lowest electronic triplet state (a3 ). The calculations were performed using the method of hyperspherical harmonics and our recent accurate double many-body expansion potential energy surface
Applying Value-Focused Thinking to a Make Versus Buy Decision
The United States Army placed emphasis on decreasing the load an individual Soldier carries by reducing the weight of ammunition through the use of polymer-cased ammunition. This paradigm shift from brass to polymer raises concerns over the implementation aspect of this new procedure into the US Army’s current ammunition production process. Our client, Project Manager Maneuver Ammunition Systems (PM-MAS) sponsored our team to analyze various candidate solutions using a methodology grounded in value-focused thinking, and recommend an implementation method to produce 7.62 mm polymer-cased ammunition at the Lake City Army Ammunition Plant (LCAAP) in Lake City, Missouri. This paper outlines the application of systems thinking concepts, various problem definition techniques and value modeling in order to effectively compare three given scenarios using a total value score versus cost analysis for each candidate solution. Our final recommendation is to implement the Buy scenario because of its total score of 63.5 and estimated cost of $14.62 million.Â
The hydrogen molecule in inclined configuration in a weak magnetic field
Highly accurate variational calculations, based on a few-parameter,
physically adequate trial function, are carried out for the hydrogen molecule
\hh in inclined configuration, where the molecular axis forms an angle
with respect to the direction of a uniform constant magnetic field ,
for and a.u. Three inclinations
are studied in detail with emphasis to
the ground state . Diamagnetic and paramagnetic susceptibilities are
calculated (for for the first time), they are in agreement
with the experimental data and with other calculations. For and
a.u. potential energy curves vs are built for each inclination,
they are interpolated by simple, two-point Pad\'e approximant
with accuracy of not less than 4 significant digits. Spectra of rovibrational
states are calculated for the first time. It was found that the optimal
configuration of the ground state for a.u. corresponds
always to the parallel configuration, , thus, it is a
state. The state remains bound for any magnetic field, becoming
metastable for , while for \,a.u. the ground state
corresponds to two isolated hydrogen atoms with parallel spins.Comment: 31 pages, 11 Tables, 7 Figures (2 new), following referee's
suggestions parts 4,5,6 essentially rewritten, to be published at Journal of
Quantitative Spectroscopy and Radiative Transfe
ExoMol molecular line lists – XX. A comprehensive line list for H3+
H3+ is a ubiquitous and important astronomical species whose spectrum has been observed in the interstellar medium, planets and tentatively in the remnants of supernova SN1897a. Its role as a cooler is important for gas giant planets and exoplanets, and possibly the early Universe. All this makes the spectral properties, cooling function and partition function of H3+ key parameters for astronomical models and analysis. A new high-accuracy, very extensive line list for H3+ called MiZATeP was computed as part of the ExoMol project alongside a temperature-dependent cooling function and partition function as well as lifetimes for excited states. These data are made available in electronic form as supplementary data to this article and at www.exomol.com
Benchmark Rovibrational Linelists and Einstein A-coefficients for the Primordial Molecules and Isotopologues
Complete benchmark rovibrational energy linelists calculated for the primordial polar molecules of the universe, namely HD+, HD, and the HeH+ isotopologues, with accuracy up to 10(-2) cm(-1) for low-lying states, are presented. To allow for these calculations to be performed, new high-accuracy potential energy curves, which include the diagonal Born-Oppenheimer adiabatic corrections and the leading relativistic corrections, are determined. Also, a new approach for calculating non-adiabatic corrections involving an effective vibrational nuclear mass obtained based on the atoms-in-molecules theory is employed. The vibrational and rotational masses are taken as being different and dependent on the nuclear distance. Accurate dipole moment curves are calculated and used to generate lists of Einstein A-coefficients. The energy linelists and the sets of Einstein A-coefficients for HD are upgrades of previous calculations including quasibound states, while for HD+ and HeH+ and its isotopologues the present results represent significant improvement over the previous calculations. The results obtained here suggest that, with the inclusion of the non-adiabatic corrections, the accuracy limit at least for low-lying states might have been reached. Thus, further progress should involve accounting for even smaller effects such as the quantum-electrodynamics corrections. The present results represent the state-of-the-art of theoretical spectroscopy of the primordial polar molecules.CAPES; Polish National Science Centre [DEC-2013/10/E/ST4/00033]; CNPqThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
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