38,445 research outputs found
Precise dipole moments and quadrupole coupling constants of the cis and trans conformers of 3-aminophenol: Determination of the absolute conformation
The rotational constants and the nitrogen nuclear quadrupole coupling
constants of cis-3-aminophenol and trans-3-aminophenol are determined using
Fourier-transform microwave spectroscopy. We examine several
and hyperfine-resolved rotational transitions for both
conformers. The transitions are fit to a rigid rotor Hamiltonian including
nuclear quadrupole coupling to account for the nitrogen nucleus. For
cis-3-aminophenol we obtain rotational constants of A=3734.930 MHz, B=1823.2095
MHz, and C=1226.493 MHz, for trans-3-aminophenol of A=3730.1676 MHz,
B=1828.25774 MHz, and C=1228.1948 MHz. The dipole moments are precisely
determined using Stark effect measurements for several hyperfine transitions to
D, D for cis-3-aminophenol and D,
D for trans-3-aminophenol. Whereas the rotational constants and
quadrupole coupling constants do not allow to determinate the absolute
configuration of the two conformers, this assignment is straight-forward based
on the dipole moments. High-level \emph{ab initio} calculations (B3LYP/6-31G^*
to MP2/aug-cc-pVTZ) are performed providing error estimates of rotational
constants and dipole moments obtained for large molecules by these theoretical
methods.Comment: 9 pages, 4 tables, 3 figures (RevTeX
Microscopic two-fluid theory of rotational constants of the OCS-H complex in He droplets
We present a microscopic quantum analysis for rotational constants of the
OCS-H complex in helium droplets using the local two-fluid theory in
conjunction with path integral Monte Carlo simulations. Rotational constants
are derived from effective moments of inertia calculated assuming that motion
of the H molecule and the local non-superfluid helium density is rigidly
coupled to the molecular rotation of OCS and employing path integral methods to
sample the corresponding H and helium densities. The rigid coupling
assumption for H-OCS is calibrated by comparison with exact calculations of
the free OCS-H complex. The presence of the H molecule is found to
induce a small local non-superfluid helium density in the second solvation
shell which makes a non-negligible contribution to the moment of inertia of the
complex in helium. The resulting moments of inertia for the OCS-H complex
embedded in a cluster of 63 helium atoms are found to be in good agreement with
experimentally measured values in large helium droplets. Implications for
analysis of rotational constants of larger complexes of OCS with multiple H
molecules in helium are discussed.Comment: 11 pages, 5 figures, accepted for publication in J. Chem. Phy
The {\it ab initio} calculation of spectra of open shell diatomic molecules
The spectra (rotational, rotation-vibrational or electronic) of diatomic
molecules due to transitions involving only closed-shell ()
electronic states follow very regular, simple patterns and their theoretical
analysis is usually straightforward. On the other hand, open-shell electronic
states lead to more complicated spectral patterns and, moreover, often appear
as a manifold of closely lying electronic states, leading to perturbations with
even larger complexity. This is especially true when at least one of the atoms
is a transition metal. Traditionally these complex cases have been analysed
using approaches based on perturbation theory, with semi-empirical parameters
determined by fitting to spectral data.
Recently the needs of two rather diverse scientific areas have driven the
demand for improved theoretical models of open-shell diatomic systems based on
an \emph{ab initio} approach, these areas are ultracold chemistry and the
astrophysics of "cool" stars, brown dwarfs and most recently extrasolar
planets. However, the complex electronic structure of these molecules combined
with the accuracy requirements of high-resolution spectroscopy render such an
approach particularly challenging. This review describes recent progress in
developing methods for directly solving the effective Schr\"odinger equation
for open-shell diatomic molecules, with a focus on molecules containing a
transtion metal. It considers four aspects of the problem: 1. The electronic
structure problem, 2. Non-perturbative treatments of the curve couplings, 3.
The solution of the nuclear motion Schr\"odinger equation, 4. The generation of
accurate electric dipole transition intensities. Examples of applications are
used to illustrate these issues.Comment: Topical Revie
Electronic spectra of polyatomic molecules with resolved individual rotational transitions
The density of rotational transitions for a polyatomic molecule is so large that in general many such
transitions are hidden under the Doppler profile, this being a fundamental limit of conventional high
resolution electronic spectroscopy. We present here the first Doppler-free cw two-photon spectrum of a
polyatomic molecule. In the case of benzene, 400 lines are observed of which 300 are due to single rotational
transitions, their spacing being weil below the Doppler profile. The resolution so achieved is 1.5 X 10'.
Benzene is a prototype planar molecule taken to have D •• symmetry in the ground as weil as in the first
excited state. From our ultra-high resolution results it is found that benzene in the excited SI state i8 a
symmetrical rotor to a high degree. A negative inertial defect is found for the excited state. The origin of this
inertial defect is discused
Relativistic Nuclear Energy Density Functionals: Mean-Field and Beyond
Relativistic energy density functionals (EDF) have become a standard tool for
nuclear structure calculations, providing a complete and accurate, global
description of nuclear ground states and collective excitations. Guided by the
medium dependence of the microscopic nucleon self-energies in nuclear matter,
semi-empirical functionals have been adjusted to the nuclear matter equation of
state and to bulk properties of finite nuclei, and applied to studies of
arbitrarily heavy nuclei, exotic nuclei far from stability, and even systems at
the nucleon drip-lines. REDF-based structure models have also been developed
that go beyond the static mean-field approximation, and include collective
correlations related to the restoration of broken symmetries and to
fluctuations of collective variables. These models are employed in analyses of
structure phenomena related to shell evolution, including detailed predictions
of excitation spectra and electromagnetic transition rates.Comment: To be published in Progress in Particle and Nuclear Physic
Rotating neutron stars: an invariant comparison of approximate and numerical spacetime models
We compare three different models of rotating neutron star spacetimes: the
Hartle-Thorne (HT) slow-rotation approximation at second order in rotation, the
exact analytic vacuum solution of Manko et al. and a numerical solution of the
full Einstein equations. We integrate the HT structure equations for five
representative equations of state. Then we match the HT models to numerical
solutions of the Einstein equations, imposing that the mass and angular
momentum of the models be the same. We estimate the limits of validity of the
HT expansion computing relative errors in the spacetime's quadrupole moment Q
and in the ISCO radii. We find that ISCO radii computed in the HT approximation
are accurate to better than 1%, even for the fastest observed ms pulsar. At the
same rotational rates the accuracy on Q is of order 20%. In the second part of
the paper we focus on the exterior vacuum spacetimes. We introduce a physically
motivated `quasi-Kinnersley' Newman-Penrose frame. In this frame we evaluate
the speciality index S, a coordinate-independent quantity measuring the
deviation of each model from Petrov Type D. On the equatorial plane this
deviation is smaller than 5%, even for the fastest rotating models. Our main
conclusion is that the HT approximation is very reliable for most astrophysical
applications.Comment: 19 pages, 9 figures, accepted in MNRAS; improved presentation, some
new analytical results in Section 5.
Photodissociation of the {HeH} molecular ion
The photodissociation cross section of the molecular ion HeH was
calculated within the Born-Oppenheimer approximation for a parallel, a
perpendicular, and an isotropic orientation of the molecular axis with respect
to the field, considering also different initial vibrational and rotational
states. The results were compared to recent data from a free-electron laser
experiment performed at the FLASH facility [H.B. Pedersen {\it et al.}, Phys.
Rev. Lett. 98, 223202, (2007)]. Within the experimental uncertainties
theoretical and experimental results are compatible with each other.Comment: 16 pages, 8 figure
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