2,050 research outputs found
A variationally computed line list for hot NH3
We present 'BYTe', a comprehensive 'hot' line list for the ro-vibrational
transitions of ammonia, 14NH3, in its ground electronic state. This line list
has been computed variationally using the program suite TROVE, a new
spectroscopically-determined potential energy surface and an ab initio dipole
moment surface. BYTe, is designed to be used at all temperatures up to 1500K.
It comprises 1137650964 transitions in the frequency range from 0 to 12000
cm-1, constructed from 1366519 energy levels below 18000 cm-1 having J values
below 36. Comparisons with laboratory data confirm the accuracy of the line
list which is suitable for modelling a variety of astrophysical problems
including the atmospheres of extrasolar planets and brown dwarfs.Comment: the paper has been submitted to MNRA
Hybrid variation-perturbation method for calculating rovibrational energy levels of polyatomic molecules
A procedure for calculation of rotation-vibration states of medium sized
molecules is presented. It combines the advantages of variational calculations
and perturbation theory. The vibrational problem is solved by diagonalizing a
Hamiltonian matrix, which is partitioned into two sub-blocks. The first,
smaller sub-block includes matrix elements with the largest contribution to the
energy levels targeted in the calculations. The second, larger sub-block
comprises those basis states which have little effect on these energy levels.
Numerical perturbation theory, implemented as a Jacobi rotation, is used to
compute the contributions from the matrix elements of the second sub-block.
Only the first sub-block needs to be stored in memory and diagonalized.
Calculations of the vibrational-rotational energy levels also employ a
partitioning of the Hamiltonian matrix into sub-blocks, each of which
corresponds either to a single vibrational state or a set of resonating
vibrational states, with all associated rotational levels. Physically, this
partitioning is efficient when the Coriolis coupling between different
vibrational states is small. Numerical perturbation theory is used to include
the cross-contributions from different vibrational states. Separate individual
sub-blocks are then diagonalized, replacing the diagonalization of a large
Hamiltonian matrix with a number of small matrix diagonalizations. Numerical
examples show that the proposed hybrid variational-perturbation method greatly
speeds up the variational procedure without significant loss of precision for
both vibrational-rotational energy levels and transition intensities. The
hybrid scheme can be used for accurate nuclear motion calculations on molecules
with up to 15 atoms on currently available computers.Comment: Molecular Physics (Handy Special Issue), in pres
MARVEL analysis of the measured high-resolution rovibronic spectra of the calcium monohydroxide radical (CaOH)
The calcium monohydroxide radical (CaOH) is an important astrophysical
molecule relevant to cool stars and rocky exoplanets, amongst other
astronomical environments. Here, we present a consistent set of highly accurate
rovibronic (rotation-vibration-electronic) energy levels for the five lowest
electronic states (\tilde{X}\,^2\Sigma^+, \tilde{A}\,^2\Pi,
\tilde{B}\,^2\Sigma^+, \tilde{C}\,^2\Delta, \tilde{D}\,^2\Sigma^+) of
CaOH. A comprehensive analysis of the published spectroscopic literature on
this system has allowed 1955 energy levels to be determined from 3204
rovibronic experimental transitions, all with unique quantum number labelling
and measurement uncertainties. The dataset covers rotational excitation up to
for molecular states below 29\,000~cm. The analysis was
performed using the MARVEL algorithm, which is a robust procedure based on the
theory of spectroscopic networks. The dataset provided will significantly aid
future interstellar, circumstellar and atmospheric detections of CaOH, as well
as assisting in the design of efficient laser cooling schemes in ultracold
molecule research and precision tests of fundamental physics
Hydrodynamic model for electron-hole plasma in graphene
We propose a hydrodynamic model describing steady-state and dynamic electron
and hole transport properties of graphene structures which accounts for the
features of the electron and hole spectra. It is intended for electron-hole
plasma in graphene characterized by high rate of intercarrier scattering
compared to external scattering (on phonons and impurities), i.e., for
intrinsic or optically pumped (bipolar plasma), and gated graphene (virtually
monopolar plasma). We demonstrate that the effect of strong interaction of
electrons and holes on their transport can be treated as a viscous friction
between the electron and hole components. We apply the developed model for the
calculations of the graphene dc conductivity, in particular, the effect of
mutual drag of electrons and holes is described. The spectra and damping of
collective excitations in graphene in the bipolar and monopolar limits are
found. It is shown that at high gate voltages and, hence, at high electron and
low hole densities (or vice-versa), the excitations are associated with the
self-consistent electric field and the hydrodynamic pressure (plasma waves). In
intrinsic and optically pumped graphene, the waves constitute quasineutral
perturbations of the electron and hole densities (electron-hole sound waves)
with the velocity being dependent only on the fundamental graphene constants.Comment: 11 pages, 6 figure
A near infrared line list for \NH: Analysis of a Kitt Peak spectrum after 35 years
A Fourier Transform (FT) absorption spectrum of room temperature NH3 in the
region 7400 - 8600 cm-1 is analysed using a variational line list and ground
state energies determined using the MARVEL procedure. The spectrum was measured
by Dr Catherine de Bergh in 1980 and is available from the Kitt Peak data
center. The centers and intensities of 8468 ammonia lines were retrieved using
a multiline fitting procedure. 2474 lines are assigned to 21 bands providing
1692 experimental energies in the range 7000 - 9000 cm-1. The spectrum was
assigned by the joint use of the BYTe variational line list and combination
differences. The assignments and experimental energies presented in this work
are the first for ammonia in the region 7400 - 8600 cm-1, considerably
extending the range of known vibrational-excited statesComment: 27 pages, 6 table, 5 figures. Accepted for publication in Journal of
Molecular Spectroscop
Collective modes of two-dimensional classical Coulomb fluids
Molecular dynamics simulations have been performed to investigate in detail
collective modes spectra of two-dimensional Coulomb fluids in a wide range of
coupling. The obtained dispersion relations are compared with theoretical
approaches based on quasi-crystalline approximation (QCA), also known as the
quasi-localized charge approximation (QLCA) in the plasma-related context. An
overall satisfactory agreement between theory and simulations is documented for
the longitudinal mode at moderate coupling and in the long-wavelength domain at
strong coupling. For the transverse mode, satisfactory agreement in the
long-wavelength domain is only reached at very strong coupling, when the cutoff
wave-number below which shear waves cannot propagate becomes small. The
dependence of the cutoff wave-number for shear waves on the coupling parameter
is obtained.Comment: 10 pages, 6 figure
Practical thermodynamics of Yukawa systems at strong coupling
Simple practical approach to estimate thermodynamic properties of strongly
coupled Yukawa systems, in both fluid and solid phases, is presented. The
accuracy of the approach is tested by extensive comparison with direct computer
simulation results (for fluids and solids) and the recently proposed
shortest-graph method (for solids). Possible applications to other systems of
softly repulsive particles are briefly discussed.Comment: Published in J. Chem. Phy
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