Search results for "chemical calculations"
showing 10 items of 12 documents
Theoretical Investigation of the Low-Energy States of CpMoCl(PMe 3 ) 2 and Their Role in the Spin-Forbidden Addition of N 2 and CO
2003
International audience; A recent computational investigation of Jahn−Teller effects in unsaturated 16-electron d4d6 [CpMLn] complexes (Abu-Hasanayn, F.; Cheong, P.; Oliff, M. Angew. Chem.2002, 41, 2120) highlighted the typical presence of two spin-triplet and two singlet states of competing stability in these complexes and pointed out the necessity to account for more than one electronic state in studies thereof. Consequently, we have reinvestigated the addition of N2 to all the four low-energy states of CpMoCl(PH3)2, a reaction for which previously only one singlet and one triplet state have been considered (Keogh, D. W.; Poli, R. J. Am. Chem. Soc.1997, 119, 2516). The present study was pe…
Preparation and molecular structures of N′-(2-heteroarylmethylidene)-3-(3-pyridyl)acrylohydrazides
2018
Abstract The crystal and molecular structures of N′-(2-furylmethylidene)-3-(3-pyridyl)acrylohydrazide and N′-(2-thienylmethylidene)-3-(3-pyridyl)acrylohydrazide are reported, and the influence of the type of the heteroatom on the aromaticity of the aromatic rings is discussed. Both molecules are nearly planar. The geometry of the acrylohydrazide arrangement is comparable to that of homologous compounds. Density functional theory (DFT) calculations were performed in order to analyze the changes in the geometry of the studied compounds in the crystalline state and for the isolated molecule. The most significant changes were observed in the values of the N–N and C–N bond lengths. The harmonic …
Deuterium hyperfine splittings in the rotational spectrum of NH2D as revealed by Lamb-dip spectroscopy
2020
Abstract In the context of radio-astronomical observations, laboratory experiments constitute a cornerstone in the interpretation of rich line surveys due to the concomitant presence of numerous emitting molecules. Here, we report the investigation of three different rotational transitions of mono-deuterated ammonia (NH2D), a species of astrophysical interest, for which the contribution of the deuterium nuclear spin to the rotational spectrum has been resolved for the first time in the millimeter- and submillimeter-wave domain. The effect of hyperfine interactions on the rotational spectrum has been unveiled by a combined theoretical and experimental approach. Quantum-chemical calculations …
Microwave, High-Resolution Infrared, and Quantum Chemical Investigations of CHBrF2: Ground and v4 = 1 States
2011
A combined microwave, infrared, and computational investigation of CHBrF(2) is reported. For the vibrational ground state, measurements in the millimeter- and sub-millimeter-wave regions for CH(79)BrF(2) and CH(81)BrF(2) provided rotational and centrifugal-distortion constants up to the sextic terms as well as the hyperfine parameters (quadrupole-coupling and spin-rotation interaction constants) of the bromine nucleus. The determination of the latter was made possible by recording of spectra at sub-Doppler resolution, achieved by means of the Lamb-dip technique, and supporting the spectra analysis by high-level quantum chemical calculations at the coupled-cluster level. In this context, the…
PRECISE LABORATORY MEASUREMENTS OF TRANS-DCOOH AND TRANS-HCOOD FOR ASTROPHYSICAL OBSERVATIONS
2011
The rotational spectra of the mono-deuterated isotopologues of trans-formic acid, trans-DCOOH and trans-HCOOD, were investigated. In the millimeter- and submillimeter-wave frequency regions the Lamb-dip technique was exploited to obtain sub-Doppler resolution and to resolve the hyperfine structure due to the deuterium and hydrogen nuclei, thus enabling the accurate determination of the corresponding hyperfine constants. The experimental determination was supported by high-level quantum-chemical calculations at the coupled-cluster level of theory using large atomic-orbital basis sets. The Lamb-dip measurements were also supplemented by THz Doppler- limited measurements in order to extend the…
The rotational spectrum of trans-DCOOD: Lamb-dip measurements, THz spectroscopy and quantum-chemical calculations
2011
Abstract The rotational spectrum of the bi-deuterated isotopologue of trans-formic acid, trans-DCOOD, was recorded at sub-Doppler resolution in the millimeter- and sub-millimeter-wave region using the Lamb-dip technique. The hyperfine structure due to the deuterium nuclei could be resolved and accurate hyperfine constants were derived. The experimental determination of the deuterium quadrupole-coupling constants was supported by high-level quantum-chemical calculations at the coupled-cluster level using large atomic-orbital basis sets. The Lamb-dip measurements were also supplemented by THz Doppler-limited measurements in order to extend the predictive capability of the available spectrosco…
Synthesis and Structural Characterization of Substituted 2-Phenacylbenzoxazoles
2013
1 H and 13C NMR spectra of eleven 2-phenacylbenzoxazoles (ketimine form) show that their CDCl3-solutions contains also (Z)-2-(benzo[d]oxazol-2-yl)-1-phenylethenols (enolimine form). Intramolecular hydrogen bonding in the latter tautomer was found to be significantly weaker than that one in respective (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines. Integrals of the 1 H NMR signals were used to evaluate the molar ratio of the tautomers. Strong electron-donating substituents were found to stabilize the ketimine tautomer. pKT (negative logarithm of the equilibrium constant, KT = [ketimine]/[enolimine]) was found to be linearly dependent on the Hammett substituent constant σ. The results of the MP2 ab…
Disclosing the emissive surface traps in green-emitting carbon nanodots
2021
Abstract The bright photoluminescence of surface-functionalized carbon nanoparticles, known as carbon nanodots (CDs), has been studied for more than a decade because of its fundamental photo-physical interest and strong technological potential. However, the essential nature of the electronic states involved in their typical light emission remains very elusive. Here, we provide conclusive evidence that surface carboxylic moieties are the key to CD fluorescence. The synergy of nanosecond and femtosecond optical studies, cryogenic fluorescence, computational investigations and chemical engineering of a strategically chosen model CD system, allows to demonstrate that their visible-light transit…
OpenMolcas: From Source Code to Insight
2019
In this article we describe the OpenMolcas environment and invite the computational chemistry community to collaborate. The open-source project already includes a large number of new developments realized during the transition from the commercial MOLCAS product to the open-source platform. The paper initially describes the technical details of the new software development platform. This is followed by brief presentations of many new methods, implementations, and features of the OpenMolcas program suite. These developments include novel wave function methods such as stochastic complete active space self-consistent field, density matrix renormalization group (DMRG) methods, and hybrid multico…
High-Pressure Properties of Wolframite-Type ScNbO4
2022
In this work, we used Raman spectroscopic and optical absorption measurements and first-principles calculations to unravel the properties of wolframite-type ScNbO4 at ambient pressure and under high pressure. We found that monoclinic wolframite-type ScNbO4 is less compressible than most wolframites and that under high pressure it undergoes two phase transitions at ∼5 and ∼11 GPa, respectively. The first transition induces a 9% collapse of volume and a 1.5 eV decrease of the band gap energy, changing the direct band gap to an indirect one. According to calculations, pressure induces symmetry changes (P2/c–Pnna–P2/c). The structural sequence is validated by the agreement between phonon calcul…