71,943 research outputs found
Rotational dynamics of CO solvated in small He clusters: a quantum Monte Carlo study
The rotational dynamics of CO single molecules solvated in small He clusters
(CO@He_N) has been studied using Reptation Quantum Monte Carlo for cluster
sizes up to N=30. Our results are in good agreement with the roto-vibrational
features of the infrared spectrum recently determined for this system, and
provide a deep insight into the relation between the structure of the cluster
and its dynamics. Simulations for large N also provide a prediction of the
effective moment of inertia of CO in the He nano-droplet regime, which has not
been measured so far
Computational spectroscopy of helium-solvated molecules: effective inertia, from small He clusters toward the nano-droplet regime
Accurate computer simulations of the rotational dynamics of linear molecules
solvated in He clusters indicate that the large-size (nano-droplet) regime is
attained quickly for light rotors (HCN, CO) and slowly for heavy ones (OCS,
NO, CO), thus challenging previously reported results. Those results
spurred the view that the different behavior of light rotors with respect to
heavy ones - including a smaller reduction of inertia upon solvation of the
former - would result from the lack of adiabatic following of the He density
upon molecular rotation. We have performed computer experiments in which the
rotational dynamics of OCS and HCN molecules was simulated using a fictitious
inertia appropriate to the other molecule. These experiments indicate that the
approach to the nano-droplet regime, as well as the reduction of the molecular
inertia upon solvation, is determined by the anistropy of the potential, more
than by the molecular weight. Our findings are in agreement with recent
infrared and/or microwave experimental data which, however, are not yet totally
conclusive by themselves.Comment: 11 pages, 13 figure
The Hyperfine Molecular Hubbard Hamiltonian
An ultracold gas of heteronuclear alkali dimer molecules with hyperfine
structure loaded into a one-dimensional optical lattice is investigated. The
\emph{Hyperfine Molecular Hubbard Hamiltonian} (HMHH), an effective low-energy
lattice Hamiltonian, is derived from first principles. The large permanent
electric dipole moment of these molecules gives rise to long range
dipole-dipole forces in a DC electric field and allows for transitions between
rotational states in an AC microwave field. Additionally, a strong magnetic
field can be used to control the hyperfine degrees of freedom independently of
the rotational degrees of freedom. By tuning the angle between the DC electric
and magnetic fields and the strength of the AC field it is possible to control
the number of internal states involved in the dynamics as well as the degree of
correlation between the spatial and internal degrees of freedom. The HMHH's
unique features have direct experimental consequences such as quantum
dephasing, tunable complexity, and the dependence of the phase diagram on the
molecular state
Microwave Heating of Water, Ice and Saline Solution: Molecular Dynamics Study
In order to study the heating process of water by the microwaves of 2.5-20GHz
frequencies, we have performed molecular dynamics simulations by adopting a
non-polarized water model that have fixed point charges on rigid-body
molecules. All runs are started from the equilibrated states derived from the
I ice with given density and temperature. In the presence of microwaves,
the molecules of liquid water exhibit rotational motion whose average phase is
delayed from the microwave electric field. Microwave energy is transferred to
the kinetic and inter-molecular energies of water, where one third of the
absorbed microwave energy is stored as the latter energy. The water in ice
phase is scarcely heated by microwaves because of the tight hydrogen-bonded
network of water molecules. Addition of small amount of salt to pure water
substantially increases the heating rate because of the weakening by defects in
the water network due to sloshing large-size negative ions.Comment: 21 pages, 13 figure
Imaging the Three-Dimensional Orientation and Rotational Mobility of Fluorescent Emitters using the Tri-Spot Point Spread Function
Fluorescence photons emitted by single molecules contain rich information regarding their rotational motions, but adapting single-molecule localization microscopy (SMLM) to measure their orientations and rotational mobilities with high precision remains a challenge. Inspired by dipole radiation patterns, we design and implement a Tri-spot point spread function (PSF) that simultaneously measures the three-dimensional orientation and the rotational mobility of dipole-like emitters across a large field of view. We show that the orientation measurements done using the Tri-spot PSF are sufficiently accurate to correct the anisotropy-based localization bias, from 30 nm to 7 nm, in SMLM. We further characterize the emission anisotropy of fluorescent beads, revealing that both 20-nm and 100-nm diameter beads emit light significantly differently from isotropic point sources. Exciting 100-nm beads with linearly polarized light, we observe significant depolarization of the emitted fluorescence using the Tri-spot PSF that is difficult to detect using other methods. Finally, we demonstrate that the Tri-spot PSF detects rotational dynamics of single molecules within a polymer thin film that are not observable by conventional SMLM
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