79 research outputs found
RichMol: A general variational approach for rovibrational molecular dynamics in external electric fields
A general variational approach for computing the rovibrational dynamics of
polyatomic molecules in the presence of external electric fields is presented.
Highly accurate, full-dimensional variational calculations provide a basis of
field-free rovibrational states for evaluating the rovibrational matrix
elements of high-rank Cartesian tensor operators, and for solving the
time-dependent Schr\"odinger equation. The effect of the external electric
field is treated as a multipole moment expansion truncated at the second
hyperpolarizability interaction term. Our fully numerical and computationally
efficient method has been implemented in a new program, RichMol, which can
simulate the effects of multiple external fields of arbitrary strength,
polarization, pulse shape and duration. Illustrative calculations of two-color
orientation and rotational excitation with an optical centrifuge of NH are
discussed
General variational approach to nuclear-quadrupole coupling in rovibrational spectra of polyatomic molecules
A general algorithm for computing the quadrupole-hyperfine effects in the
rovibrational spectra of polyatomic molecules is presented for the case of
ammonia (NH). The method extends the general variational approach TROVE by
adding the extra term in the Hamiltonian that describes the nuclear quadrupole
coupling, with no inherent limitation on the number of quadrupolar nuclei in a
molecule. We applied the new approach to compute the
nitrogen-nuclear-quadrupole hyperfine structure in the rovibrational spectrum
of NH. These results agree very well with recent experimental spectroscopic
data for the pure rotational transitions in the ground vibrational and
states, and the rovibrational transitions in the , , ,
and bands. The computed hyperfine-resolved rovibrational spectrum
of ammonia will be beneficial for the assignment of experimental rovibrational
spectra, further detection of ammonia in interstellar space, and studies of the
proton-to-electron mass variation
Detecting chirality in molecules by linearly polarized laser fields
A new scheme for enantiomer differentiation of chiral molecules using a pair
of linearly polarized intense ultrashort laser pulses with skewed mutual
polarization is presented. The technique relies on the fact that the
off-diagonal anisotropic contributions to the electric polarizability tensor
for two enantiomers have different signs. Exploiting this property, we are able
to excite a coherent unidirectional rotation of two enantiomers with a {\pi}
phase difference in the molecular electric dipole moment. The approach is
robust and suitable for relatively high temperatures of molecular samples,
making it applicable for selective chiral analysis of mixtures, and to chiral
molecules with low barriers between enantiomers. As an illustration, we present
nanosecond laser-driven dynamics of a tetratomic non-rigid chiral molecule with
short-lived chirality. The ultrafast time scale of the proposed technique is
well suited to study parity violation in molecular systems in short-lived
chiral states
ExoMol molecular line lists - XXVII: spectra of C2H4
A new line list for ethylene, CH is presented. The line
list is based on high level ab initio potential energy and dipole moment
surfaces. The potential energy surface is refined by fitting to experimental
energies. The line list covers the range up to 7000 cm (1.43 m)
with all ro-vibrational transitions (50 billion) with the lower state below
5000 cm included and thus should be applicable for temperatures up to
700 K. A technique for computing molecular opacities from vibrational band
intensities is proposed and used to provide temperature dependent cross
sections of ethylene for shorter wavelength and higher temperatures. When
combined with realistic band profiles (such as the proposed three-band model),
the vibrational intensity technique offers a cheap but reasonably accurate
alternative to the full ro-vibrational calculations at high temperatures and
should be reliable for representing molecular opacities. The CH line
list, which is called MaYTY, is made available in electronic form from the CDS
Field-induced diastereomers for chiral separation
A novel approach for the state-specific enantiomeric enrichment and the
spatial separation of enantiomers is presented. Our scheme utilizes techniques
from strong-field laser physics, specifically an optical centrifuge in
conjunction with a static electric field, to create a chiral field with defined
handedness. Molecular enantiomers experience unique rotational excitation
dynamics and this can be exploited to spatially separate the enantiomers using
electrostatic deflection. Notably, the rotational-state-specific enantiomeric
enhancement and its handedness is fully controllable. To explain these effects,
we introduce the conceptual framework of
of a chiral molecule and perform robust quantum mechanical simulations on the
prototypical chiral molecule propylene oxide (CHO), for which ensembles
with an enantiomeric excess of up to were obtained
Controlling rotation in the molecular-frame with an optical centrifuge
We computationally demonstrate a new method for coherently controlling the
rotation-axis direction in asymmetric top molecules with an optical centrifuge.
Appropriately chosen electric-field strengths and the centrifuge's acceleration
rate allow to generate a nearly arbitrary rotational wavepacket. For DS and
2H-imidazole (CHN) we created wavepackets at large values of the
rotational quantum number with the desired projections of the total angular
momentum onto two of the molecules' principal axes of inertia. One application
of the new method is three-dimensional alignment with a molecular axis aligned
along the laser's wave vector, which is important for the three-dimensional
imaging of molecules yet not accessible in standard approaches. The
simultaneous orientation of the angular momentum in the laboratory frame and in
the molecular frame could also be used in robust control of scattering
experiments
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