The accurate knowledge of electronic properties is important for creating and manufacturing ultracold molecules. We report here the ab initio quantum chemistry calculations on the properties of alkali-metal-ytterbium AM-Yb (AM = Li, Na, K, Rb, Cs) and alkaline-earth-metal-ytterbium AEM-Yb (AEM = Be, Mg, Ca, Sr, Ba) molecules for their electronic ground state. The potential energy curves (PECs) and permanent dipole moments (PDMs) are calculated on the basis of the multireference configuration interaction (MRCI) level of theory, where the core-valence correlations and scalar relativistic effects are included. The related spectroscopic constants are also determined. The results demonstrate that the dissociation energies and PDMs of AEM-Yb are smaller than those of AM-Yb molecules, and an interesting trend of the dissociation energy has been observed. This work provides favorable information for the experimental study of forming ultracold molecules via photoassociation technique.
In this paper, we systematically investigate the electronic structure for the (2)Σ(+) ground state of the polar alkali-metal-alkaline-earth-metal molecules BaAlk (Alk = Li, Na, K, Rb, and Cs). Potential energy curves and permanent dipole moments (PDMs) are determined using power quantum chemistry complete active space self-consistent field and multi-reference configuration interaction methods. Basic spectroscopic constants are derived from ro-vibrational bound state calculation. From the calculations, it is shown that BaK, BaRb, and BaCs molecules have moderate values of PDM at the equilibrium bond distance (BaK:1.62 D, BaRb:3.32 D, and BaCs:4.02 D). Besides, the equilibrium bond length (4.93 Å and 5.19 Å) and dissociation energy (0.1825 eV and 0.1817 eV) for the BaRb and BaCs are also obtained.
In a microwave field, the dielectric
properties, molecular structures,
and hydrogen bonding dynamics of glycerol in its mixtures with water
were determined by the molecular dynamics simulation method. The dipole–dipole
correlation of glycerol is linked to the field intensity of microwaves.
The results show that as the field intensity is increased, even glycerol
in the second coordination shell can become correlated with each other.
The structures of up to 35 glycerol molecules are observed. More than
that, it was observed that lifetimes of glycerol–glycerol hydrogen
bonds were prolonged, while the average hydrogen bond number was also
increased. Besides, the structures in a strong microwave field mimic
the weak C–H⋯O hydrogen bonds seen in high-glycerol
concentration mixtures, yet the concentration is lower. These results
indicate that with the assistance of the microwave field, glycerol
molecules become concentrated and are more likely to establish stable
interactions with others. As a consequence, the spherical clusters
composed by glycerol molecules in our nanosheet synthesis experiment
are easier to form.
Energy efficiency has always been
an inherent problem of microwave
heating. In this work, the higher heating efficiency of the elliptically
polarized microwave electric field is investigated via MD simulations,
aiming to examine the multidirectional polarization effect during
microwave heating. The MD results show that the heating efficiency
growth rates of EtOH, AcOH, DMSO, H2O, and DMF are 3.17%,
3.92%, 4.14%, 5.00%, and 27.06% sequentially larger with the elliptically
polarized microwave electric field (EF) than those with the linearly
polarized microwave EF. Energy analyses indicate that the utilization
rate of microwave energy would be increased of the elliptically polarized
microwave EF with the same electric field intensities. The higher
decay speed of the rotation autocorrelation function curves of elliptically
polarized EF presents that the sample molecules do have a more frequent
rotational motion to align with the varying polarization directions.
Additionally, dielectric properties analysis gave the relation between
the heating efficiency growth rate and the loss tangent of the samples.
This microwave heating method is expected to be a new route to improve
the microwave heating efficiency.
Microwave
nonthermal effect in chemical reactions is still an uncertain problem.
In this work, we
have studied the spatial orientation and kinetic energy of reactive
site collision between benzyl chloride and piperidine molecules in
substitution reaction under microwave irradiation using the molecular
dynamics simulation. Our results showed that microwave polarization
can change the spatial orientation of reactive site collision. Collision
probability between the Cl atom of the C–Cl group of benzyl
chloride and the H atom of the N–H group of piperidine increased
by up to 33.5% at an effective spatial solid angle (θ, φ)
of (100∼110°, 170∼190°) under microwave irradiation.
Also, collision probability between the C atom of the C–Cl
group of benzyl chloride and the N atom of the N–H group of
piperidine also increased by up to 25.6% at an effective spatial solid
angle (θ, φ) of (85∼95°, 170∼190°).
Moreover, the kinetic energy of collision under microwave irradiation
was also changed, that is, for the collision between the Cl atom of
the C–Cl group and the H atom of the N–H group, the
fraction of high-energy collision greater than 6.39 × 10–19 J increased by 45.9 times under microwave irradiation,
and for the collision between the C atom of the C–Cl group
and the N atom of the N–H group, the fraction of high-energy
collision greater than 6.39 × 10–19 J also
increased by 29.2 times. Through simulation, the reaction rate increased
by 34.4∼50.3 times under microwave irradiation, which is close
to the experimental increase of 46.3 times. In the end, spatial orientation
and kinetic energy of molecular collision changed by microwave polarization
are summarized as the microwave postpolarization effect. This effect
provides a new insight into the physical mechanism of the microwave
nonthermal effect.
The
molecular mechanism of the microwave nonthermal effect is still
not clear. This work investigated the spatial orientation and kinetic
energy of active site collision of carnosine, a natural bioactive
dipeptide, under the weak microwave irradiation using the molecular
dynamics simulation. Our results showed the influences of the temperature,
microwave intensity, microwave frequency, and microwave polarization
mode (linear polarization and circular polarization) on the spatial
orientation and kinetic energy of active site collision of carnosine.
First, under the constant intensity and frequency of linear polarization
microwave irradiation, the increment of the collision probability
between the 6N atom of carnosine and the 28H atom of the other carnosine
at effective space angle decreases from 85.0% to 3.5% with increasing
temperature. Second, with the increase of microwave intensity, the
change of spatial orientation and kinetic energy becomes more and
more significant. However, the change of circular polarization microwaves
on the spatial orientation and kinetic energy of collision is weaker
than that of linear polarization. Third, under the constant intensity
of linear polarization microwave irradiation, the collision probability
between the 6N atom and the 28H atom at effective space angle decreases
from 70.2% to 14.7% with increasing frequency. Finally, under the
microwave polarization, the spatial orientation and kinetic energy
of molecular collision are changed, which is summarized as the microwave
postpolarization effect (MWPPE). The dependence of MWPPE on temperature,
microwave intensity, microwave frequency, and polarization mode is
very complicated. In the end, this effect can provide a new insight
into the molecular mechanism of the microwave nonthermal effect.
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