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"Chemical physics"
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Long and isolated graphene nanoribbons by on-surface polymerization on Au(111)
Low electronic gap graphene nanoribbons (GNRs) are used for the fabrication of nanomaterial-based devices and, when isolated, for mono-molecular electronics experiences, for which a well-controlled length is crucial. Here, an on-surface chemistry protocol is monitored for producing long and well-isolated GNR molecular wires on an Au(111) surface. The two-step Ullmann coupling reaction is sequenced in temperature from 100 °C to 350 °C by steps of 50 °C, returning at room temperature between each step and remaining in ultrahigh vacuum conditions. After the first annealing step at 100 °C, the monomers self-organize into 2-monolayered nano-islands. Next, the Ullmann coupling reaction takes place in both 1st and 2nd layers of those nano-islands. The nano-island lateral size and shape are controlling the final GNR lengths. Respecting the above on-surface chemistry protocol, an optimal initial monomer coverage of ~1.5 monolayer produces isolated GNRs with a final length distribution reaching up to 50 nm and a low surface coverage of ~0.4 monolayer suitable for single molecule experiments.
The on-surface synthesis of graphene nanoribbons with control over their length and final surface coverage is desirable for electronic applications. Here, the authors outline a protocol to produce long and isolated graphene nanoribbons on an Au(111) surface, achieving lengths of up coverage down to ~0.4 monolayer, of potential value for mono-molecular electronics. to 50 nm and a low surface coverage down to ~0.4 monolayer, of potential value for mono-molecular electronics.
Journal Article
Sciencia : mathematics, physics, chemistry, biology, and astronomy for all
\"From the structure of the cosmos to that of the human body, the discoveries of science over the past few hundred years have been remarkable. Sciencia spans the realms of mathematics, physics, chemistry, biology, and astronomy, offering an invaluable introduction to each. Curious about quarks, quasars, and the fantastic universe around you? Ever wanted to explore a mathematical proof? Need an introduction to biochemistry? Beautifully illustrated with engravings, woodcuts, and original drawings and diagrams, Sciencia will inspire inquisitive readers of all ages to appreciate the interconnected knowledge of the modern sciences\"--Page 4 of cover.
Book
Formation of the methyl cation by photochemistry in a protoplanetary disk
Forty years ago, it was proposed that gas-phase organic chemistry in the interstellar medium can be initiated by the methyl cation CH
3
+
(refs.
1
–
3
), but so far it has not been observed outside the Solar System
4
,
5
. Alternative routes involving processes on grain surfaces have been invoked
6
,
7
. Here we report James Webb Space Telescope observations of CH
3
+
in a protoplanetary disk in the Orion star-forming region. We find that gas-phase organic chemistry is activated by ultraviolet irradiation.
JWST observations of CH
3
+
in a protoplanetary disk in the Orion star-forming region are reported showing that gas-phase organic chemistry in the interstellar medium is activated by ultraviolet irradiation and the methyl cation.
Journal Article
Analytical energy levels of the Schrödinger equation for the improved generalized Pöschl–Teller oscillator with magnetic vector potential coupling
In this study, a Pekeris-type approximation scheme was developed to solve the radial Schrödinger equation with and without external magnetic vector potential field. Using the proposed model, the radial Schrödinger equation was solved with the improved generalized Pöschl–Teller (IGPT) potential in the presence of external magnetic and Aharonov–Bohm (AB) flux fields. The parametric Nikiforov–Uvarov solution technique was used to derive equation for bound-state energies. The obtained equation was applied to diatomic molecules including Na
2
(5
1
Δ
g
), K
2
(a
3
Σ
u
+
),
7
Li
2
(6
1
Π
u
) and NaLi (A
1
Σ
+
). The study shows that at moderate field strengths, the presence of the magnetic field gives rise to partially degenerate energy states in the system while the AB field leads nondegenerate energy spectrum. In the absence of the magnetic and AB fields, the mean absolute percentage deviation (MAPD) of computed energies from experimental data 0.7217%, 0.5286%, 0.5109% and 1.7537% for the molecules. The MAPD obtained with the equation for ro-vibrational energies of the IGPT potential are 0.7151%, 0.5278%, 0.4934% and 1.7464%. The results obtained for bound-state energies are in good agreement with existing literature on IGPT potential.
Graphical Abstract
Journal Article
Electron-driven processes for perfluoronitriles
We report the results of the study on electron-driven molecular processes for the perfluoronitriles, C
3
F
5
N and C
4
F
7
N for a wide energy range, from the ionisation potential to 5000 eV. These compounds have been shown to have extremely low global warming potential, suggesting they could be useful in gas discharges and plasma reactors. Calculations of ionisation cross sections (
Q
ion
) are made using the complex scattering potential-ionisation contribution (CSP-ic) method and are shown to be in good agreement with the available data. Elastic (
Q
el
), inelastic (
Q
inel
) and total (
Q
T
) cross sections are computed through spherical complex optical potential formalism. We have recently developed two-parameter semi-empirical method (2p-SEM) for large molecules with 55 < Z < 95 to report
Q
el
and
Q
T
. This work is a maiden report of
Q
el
and
Q
T
for C
3
F
5
N and C
4
F
7
N. We present various correlation studies between the cross sections and target parameters, leading to a prediction of polarizability. We have derived dielectric constant using number density and molar mass and have correlated
Q
ion
(max) with dielectric constant.
Graphical abstract
Journal Article
Conservation of the number of nodes in the wavefunctions of one-electron diatomic quasimolecules
The conservation of the number of nodes in the wavefunctions of one-electron diatomic quasimolecules is treated. The elaborated approach is focused on the behavior of separation constants and their relationship to the number of nodes as the distance between nuclei varies. By examining the separation constants for quasimolecules with different nuclear charges, we demonstrate the robustness of the number of nodes across different states and separations without explicitly defining the wavefunctions themselves.
Graphical abstract
Journal Article
Photo double-ionization of CO2 studied by photoelectron-photoelectron coincidence experiments at 20 eV excess energy in equal energy sharing conditions
The Triple-Differential Cross Section (TDCS) for the Photo Double-Ionization of carbon dioxide molecule to the CO
2
2+
X
3
Σ
g
−
ground state has been measured at 20 eV excess energy. In the experiment the coincidence angular distributions of the two photoelectrons, where the direction of one photoelectron has been fixed at 0, 30 and 60° with respect to the direction of the polarization of the incident radiation, have been measured for a condition where the two photoelectrons equally share the excess energy. Care has been taken to perform the measurements with an energy resolution which enabled to isolate the TDCS of the X
3
Σ
−
g
ground state of the dication. An appreciable contribution to TDCS at a relative angle θ
12
= 180° has been observed and attributed to a favorite symmetry of the wavefunction of the two ejected electrons.
Graphical abstract
TDCS of CO
2
measures at photon energy 57.7eV, θ
1
=0, 30 and 60° and equal energy sharing of 10 eV are reported as black dots. Panels (a) and (c) report the TDCS as calculated by Alwan et al. (J Phys B: At Mol Opt Phys 48:185203, 2015) using the charge in the Sommerfeld parameters for the oxygen atom of 0.2 (black full curve) and 0.8 (ref full curve). The blue full curve in panels (d)-(f) is the fit to the experiments with the helium=like model by Reddsih and Feaging (J Phys B: At Mol Opt Phys 32:2473, 1999).
Journal Article
Nonrelativistic bound-state energy spectrum and persistent current in the modified Rosen–Morse oscillator confined to a 2D electromagnetic potential field
This research solves the Schrödinger equation with the modified Rosen–Morse oscillator (MRMO) in the presence of external magnetic and Aharonov–Bohm flux fields. The approximate equation for the bound-state energy spectrum is derived using the parametric Nikiforov-Uvarov solution recipe and a Pekeris-type approximation scheme. The expression for the bound-state energy spectrum is used to construct the formula for persistent current in the MRMO. The obtained equations are applied to diatomic systems including N
2
+
(X
1
Σ
g
+
), Rb
2
(X
1
Σ
g
+
) and SO (X
2
Σ
−
) molecules. By excluding the magnetic and AB fields, the number of excited bonded states obtained for the molecules are 59, 126, and 68, respectively. With the aid of the equation for the energy spectrum, approximate energy eigenvalues are computed for the molecules, and the results obtained agree with the data generated by numerical methods. The study also reveals that the current in the MRMO is linearly related to the magnetic quantum number. The results obtained in this study are in good agreement with the literature on diatomic molecules.
Graphical abstract
Journal Article
Quantum states of H2+ and H2 in an icosahedral potential well
We investigate the potential energy surfaces (PESs) of the hydrogen-based cation H
2
+
and the neutral molecule H
2
confined inside an infinite potential well in the shape of a regular icosahedron. The numerical computations are performed using the diffusion Monte Carlo method and are based on an analytical technique for obtaining simple equations of the surfaces of convex polyhedra proposed by S. Onaka. Different states and different orientations of the molecules inside the confining potential well, as well as various sizes of the latter, are studied. We provide a detailed symmetry analysis and consistent labeling of the H
2
+
states considered. The results show that the icosahedral confinement is closely isotropic in its inner region, leading to PESs that develop pronounced minima, as in the case of simpler confinement geometries. Shape-specific effects can be evidenced when the nuclei are in contact with the confining wall.
Journal Article