2,619 research outputs found
ARE LINEAR MOLECULES REALLY LINEAR? II. RE-INTERPRETATION OF EXPERIMENTAL B0-VALUES.
No full textAs discussed in the preceding talk, any linear triatomic molecule will be observed as being ``bent'' on ro-vibronic average in any ro-vibronic state.\footnote{T.~Hirano, U.~Nagashima, {\it J. Mol. Spectrosc.}, {\bf 314}, 35--47 (2015)}%
\footnote{T.~Hirano, U.~Nagashima, P.~Jensen, {\it J. Mol. Spectrosc.} {\bf 343}, 54--61 (2018).}\footnote{T.~Hirano, U.~Nagashima, P.~Jensen, {\it J. Mol. Spectrosc.} (2018), https://doi.org/10.1016/j.jms.2017.12.011; and references therein.}
Experimentally derived constants are the results of the ``observation''
of Nature. This suggests that the observed values are in fact those for the ro-vibrationally averaged bent structures.
The easiest way to check this proposition is to interpret
the set of values of isotopologues taking the bond-angle as a ``variable,''
discarding the preconceived, conventional notion that the ro-vibrationally averaged
bond angle of a linear molecule is 180.
We have shown in previous publications that bond length values derived from a set of
experimental values under the assumption of a linear structure, is not
the ro-vibrationally averaged bond lengths, but their projections
onto the molecular axis. Therefore, when the projection angle is not accounted for,
the bond length values obtained from the values may differ significantly
from the averaged bond lengths.
We will show how we can derive physically sound ro-vibrational structures
from the experimentally reported values, taking the FeCO, NCS, HCO, HCN,
and C molecules as examples. The averaged bond-angle deviations from the linearity,
derived from experimentally reported values of multiple
isotopologues, are 7.8, 9.5, 12.5, 14.3, and 23.4, respectively, for NCS, FeCO, HCO, HCN, and C
in their respective
vibrational ground states.
Thus, we can conclude that both theoretically (as described in the preceding talk)
and experimentally (as shown here), the ro-vibrationally averaged structure
of a linear molecule is observed as being bent
ARE LINEAR MOLECULES REALLY LINEAR? I. THEORETICAL PREDICTIONS
No full textIn spectroscopic parlance, a linear triatomic molecule is one whose potential energy
minimum occurs at
a linear geometry. We have recently discussed\footnote{T.~Hirano, U.~Nagashima, {\it J. Mol. Spectrosc.}, {\bf 314}, 35--47 (2015)}%
\footnote{T.~Hirano, U.~Nagashima, P.~Jensen, {\it J. Mol. Spectrosc.} {\bf 343}, 54--61 (2018).}\footnote{T.~Hirano, U.~Nagashima, P.~Jensen, {\it J. Mol. Spectrosc.} (2018), https://doi.org/10.1016/j.jms.2017.12.011; and references therein.}
that any linear triatomic molecule will be observed as being ``bent'' on ro-vibronic average
in any ro-vibronic state. As quantum mechanics asserts, we have to characterize Nature through ``observation.''
Theoretically we make observations of molecular structures by calculating the expectation values of the structural parameters
over the relevant ro-vibronic wavefunctions.
In computational molecular spectroscopy studies,
we have shown that for many linear triatomic molecules such as FeNC, FeCN, BrCN, CoCN, NiCN, CsOH, FeCO, and NCS, the ro-vibrationally averaged structure
(zero-point structure, for example) is slightly bent with a bond angle supplement 180 (A-B-C)
[where
(A-B-C) is the bond angle]
in the range from 7.5 (NCS) to 22.5 (C).
We have also described the theoretical background for this fact
using a Laguerre-Gauss type wavefunction for the doubly degenerate bending oscillator;
the average ``bentness'' is basically caused by the inseparability of
the bending motion from the free rotation about the molecular axis.
Our finding is in contradiction to the well-established paradigm in spectroscopy
that the ro-vibrationally averaged structure of a linear molecule is linear.
In particular, it throws doubt on the
so-called structures routinely determined
for linear triatomic molecules under the \textit{a priori} assumption
that ro-vibrationally averaged bond-angle of a linear molecule should be 180.
In the following talk, we discuss how experimentally derived rotational-constant values
are to be interpreted
RO-VIBRATIONALLY AVERAGED STRUCTURE OF 2Π NCS: RE-INTERPRETATION OF THE B0 VALUES
No full textWe have constructed \textit{ab initio} 3D potential energy surfaces (PESs)
for NCS
in core-valence SDCI+/[aCVQZ(N,C,S)] calculations.
The value predicted from these PESs deviates only 0.05\%\
from the corresponding experimental values for NCS and NCS. Since we have quite accurate 3D PESs,
we can determine both the equilibrium structure and the structure accurately:
(N--C) = 1.1778~\AA, (C--S) = 1.6335~\AA,
and (N--C--S) = 180.
The ro-vibrationally averaged
structure, determined as expectation values over DVR3D wavefunctions, has
(N--C) = 1.1836~\AA,
(C--S) = 1.6356~\AA, and
(N--C--S) = 172.5.
The 3D PESs show that the NCS has its potential energy minimum
at a linear configuration, and hence it is a ``linear molecule.''
Experimentally, values are reported for two isotopologues only.\footnote{A.~Maeda, H.~Habara, T.~Amano, {\it Mol. Phys.}, {\bf 105}, 477--495 (2007).} Using the expectation values given above as the initial guess,
a bent structure having an (N--C--S)
of 172.2 is deduced from the experimentally reported values for NCS and NCS. It shows that the linear molecule NCS has a ``bent'' ro-vibrationally averaged structure, confirming our previous predictions:\footnote{T.~Hirano, U.~Nagashima, {\it J. Mol. Spectrosc.}, {\bf 314}, 35--47 (2015); %
T.~Hirano, U.~Nagashima, P.~Jensen, {\it J. Mol. Spectrosc.} {\bf 343}, 54--61 (2018).} any linear molecule is observed as being bent on ro-vibrational average. See Ref.~ \footnote{T.~Hirano, U.~Nagashima, P.~Jensen, {\it J. Mol. Spectrosc.} (2018), https://doi.org/10.1016/j.jms.2017.12.011.} for further discussion of this molecule.
NCS is a typical Renner molecule.
The Renner spectroscopy of this molecule will be presented in a separate talk.\footnote{J.~Freund et al, ``Computational spectroscopy of NCS in the Renner-degenerate Electronic state .''
Taiwanaptera Heiss & Nagashima 2008
No full textKey to Taiwanaptera species 1 Apex of triangular scutellum-like projection of mesonotum narrow, subacute; its surface transversely rugose without distinct elevation; anterolateral angles of pronotum nearly rectangular. Taiwan, Japan, Ryukyu (Figs 5, 11)................................................................................... T. glabra Heiss & Nagashima, 2008 – Apex of triangular scutellum-like projection of mesonotum wider and rounded, its surface distinctly medially raised; anterolateral angles of pronotum produced...................... 2 2 Scutellar ridge as wide as diameter of lateral sclerites and of same height on whole length; antennae longer, about twice as long as width of head; postocular lobes with distinct lateral tubercle; spiracles II–IV ventral and not visible from above, V–VII lateral and visible. China: Guangxi (Figs 6, 9).......................................................... T. guangxiana sp. nov. – Scutellar ridge distinctly narrower than diameter of lateral sclerites, depressed at middle; antennae about 1.8–1.9 times as long as width of head; postocular lobes granulate; spiracles II–III ventral and not visible from above, IV sublateral and V–VII lateral and visible. China: Yunnan (Figs 7, 10)............................................................... T. montana sp. nov.Published as part of Bai, Xiaoshuan, Heiss, Ernst & Cai, Wanzhi, 2017, A new genus and three new species of apterous Carventinae from China (Hemiptera: Heteroptera: Aradidae), pp. 35-46 in Acta Entomologica Musei Nationalis Pragae (suppl.) (suppl.) 57 (1) on page 41, DOI: 10.1515/aemnp-2017-0056, http://zenodo.org/record/448673
Sensitive Multi-Core Fiber by Reduced-Noise In-Fiber Interferometric Sensor
No full textUncoupled-core multicore fiber becomes sensitive to vibrations by a Michelson interferometer embedded inside the fiber. By employing two cores in a 5.2-km 4-core fiber, environmental noise is strongly reduced with respect to the same configuration implemented with a fiber pair in a telecom cable
COMPUTATIONAL SPECTROSCOPY OF NCS IN THE RENNER-DEGENERATE ELECTRONIC STATE X̃ 2Π
No full text NCS is a Renner-degenerate linear molecule
whose rovibronic spectrum is greatly complicated by the Renner effect and
all-pervading resonances. As an alternative avenue to understanding this spectrum,
we have calculated values of the ro-vibronic energies, intensities,
and rotational constants by direct numerical solution of the rovibronic Schr\"odinger equation
with the RENNER program.\footnote{J.~Freund,
S.~C.~Galleguillos Kempf, P.~Jensen, U.~Nagashima, T.~Hirano, {\it J. Mol. Spectrosc.} {\bf 345}, 31–38 (2018). DOI: 10.1016/j.jms.2017.11.010;
T.~Hirano, U.~Nagashima, P.~Jensen, J. Mol. Spectrosc., (2018), https://doi.org/10.1016/j.jms.2017.12.011.}
All values obtained are
in good agreement with the available experimental data.
Ro-vibronic spectra are also simulated.
The Renner calculations are
based on three-dimensional potential energy surfaces
and dipole moment surfaces computed {\it ab initio}
for NCS in the electronic ground state at the
core-valence, full-valence MR-SDCI+Q/[aug-cc-pCVQZ(N, C, S)]
level of theory
Study on transmission technology using optical fractional discrete Fourier transform device for optical OFDM
No full textRo-vibrationally Averaged Molecular Structure Of Benzene Ii. Computational Molecular Spectroscopy Study.
No full textSince the 30 dimensional potential energy surface is beyond our reach, we tried to disclose why the C--H and C--D
bond-lengths are observed as being almost identical\footnote{S. Kunishige, M. Baba, et al., J. Chem. Phys. {\bf 143},
244302 (2015).} in terms of C--H stretching (), out-of-plane (), and
in-plane () local modes with respect to the C--H(D) bond
in the virtual triatomic molecules [CH(D)]--[C]--H(D).
The potential energy surface was determined at the valence-CCSD(T)/[aVQZ (H,C)] level of theory,
and -structure was determined from the DVR3D wavefuctions in Discrete Variable Representation.
The virtual [CH(D)]--[C]--H(D) molecule has its energy minimum at the
linear configuration, so that our theory for linear triatomics\footnote{T. Hirano, U. Nagashima, P. Jensen,
J. Mol. Spectrosc. \textbf{343}, 54 (2018);
T. Hirano, U. Nagashima, M. Baba, J. Mol. Spectrosc. \textbf{369}, 111252 (2020); and references therein.} can be
applied.
The C--H(D) stretching local mode () gives,
as usual, longer C--H than C--D bond-lengths
due to its anharmonicity.
However, in both and modes,
the vibrationally averaged bond-length projected onto the principal axis is shorter
for C--H than for C--D
due to the larger averaged bending angle for the former bond.
When we consider bond-lengths projected onto the - principal axis plane, ,
these antithetical factors, i.e., one in the mode against
the others in and modes,
nearly cancel ( (C--H) (C--D) 0.0004 {\AA}),
resulting in almost the same C--H and C--D bond lengths as is experimentally reported.
The vibrationally averaged structure of benzene in the zero-point vibration state
is predicted to be planar, but non-flat in the peripheral C--H bonds moiety,
which is confirmed from the theoretical and experimental values of the inertial defect.Made available in DSpace on 2021-09-24T21:09:18Z (GMT). No. of bitstreams: 2
5411.pdf: 26186 bytes, checksum: b9586d1cbf1d85d5dc47d0ff4a0ee46a (MD5)
license.txt: 4802 bytes, checksum: 58353f9dd6876860dd5221f3d7872a95 (MD5)
Previous issue date: 2021-06-25Made available in DSpace on 2022-01-21T16:09:19Z (GMT). No. of bitstreams: 4
5411.pdf.txt: 2195 bytes, checksum: 19a54c8dd6253c2aead98ac730088c68 (MD5)
license.txt: 4802 bytes, checksum: 58353f9dd6876860dd5221f3d7872a95 (MD5)
5411.pdf: 26186 bytes, checksum: b9586d1cbf1d85d5dc47d0ff4a0ee46a (MD5)
FK13_5411.pdf: 201470 bytes, checksum: f503613ca0ec2d2bb0890b6dbe305a93 (MD5)
Previous issue date: 2021-06-2
Performance evaluation of fractional OFDM for extending transmission distance without reducing spectral efficiency
No full textThe performance of a fractional orthogonal frequency division multiplexing (FrOFDM) system is examined considering spectral efficiency (SE). While FrOFDM can reduce peak-to-average power ratio, which is a drawback in OFDM, its bandwidth is expanded. Simulations were performed to evaluate the increasing amount of transmission distance from the signal-to-noise ratio of the received signals with keeping the best SE of OFDM. Simulation results show that FrOFDM can increase the transmission distance without reducing SE
- …
