scholarly journals H 2 O−N 2 collision-induced absorption band intensity in the region of the N 2 fundamental: ab initio investigation of its temperature dependence and comparison with laboratory data

2012 ◽  
Vol 370 (1968) ◽  
pp. 2691-2709 ◽  
Author(s):  
Yu. I. Baranov ◽  
I. A. Buryak ◽  
S. E. Lokshtanov ◽  
V. A. Lukyanchenko ◽  
A. A. Vigasin
Keyword(s):  
Absorption Band ◽  
Ab Initio ◽  
Temperature Dependence ◽  
Laboratory Data ◽  
Basis Set ◽  
Band Intensity ◽  
Intermolecular Potential ◽  
Laboratory Evaluation ◽  
Induced Absorption ◽  
Absorption Band Intensity

The present paper aims at ab initio and laboratory evaluation of the N 2 collision-induced absorption band intensity arising from interactions between N 2 and H 2 O molecules at wavelengths of around 4 μm. Quantum chemical calculations were performed in the space of five intermolecular coordinates and varying N−N bond length using Møller–Plesset perturbation and CCSD(T) methods with extrapolation of the electronic energy to the complete basis set. This made it possible to construct the intermolecular potential energy surface and to define the surface of the N−N dipole derivative with respect to internal coordinate. The intensity of the nitrogen fundamental was then calculated as a function of temperature using classical integration. Experimental spectra were recorded with a BOMEM DA3-002 FTIR spectrometer and 2 m base-length multipass White cell. Measurements were conducted at temperatures of 326, 339, 352 and 363 K. The retrieved water–nitrogen continuum significantly deviates from the MT_CKD model because the relatively strong nitrogen absorption induced by H 2 O was not included in this model. Substantial uncertainties in the measurements of the H 2 O−N 2 continuum meant that quantification of any temperature dependence was not possible. The comparison of the integrated N 2 fundamental band intensity with our theoretical estimates shows reasonably good agreement. Theory indicates that the intensity as a function of temperature has a minimum at approximately 500 K.

scholarly journals Intermolecular Lennard-Jones (22-11)Potential Energy Surface in Dimer of N8 Cubane Cluster

2017 ◽  
Vol 59 (2) ◽  
Author(s):  
Jamshid Najafpour
Keyword(s):  
Potential Energy ◽  
Potential Energy Surface ◽  
Ab Initio ◽  
Density Functional ◽  
Energy Surface ◽  
Separation Distance ◽  
Basis Set ◽  
Intermolecular Potential ◽  
Basis Set Superposition Error ◽  
Lennard Jones

<p>We have calculated the intermolecular potential energy surface (IPES) of the dimer of cubic N8 cluster using <em>ab initio </em>and the density functional theory (DFT) calculations. The <em>ab initio </em>(HF/3- 21G(d)) and DFT (B3LYP/6-31G(d) and aug-cc-pVDZ) calculations were performed for two relative orientations of N8-N8 system as a function of separation distance between the centers of cubic N8 clusters. In this research, the IPES, <em>U</em>(<em>r</em>), of the N8-N8 system is studied, where the edge of N8 approaches to face or edge of the other considered N8. Then, the Lennard-Jones (12-6) and (22-11) adjustable parameters are fitted to the computed interaction energies for edge-face and edge-edge orientations. In this research for the first time, the IPESs proportionated to the Lennard-Jones (22-11) potential are derived that are compatible with the computed IPES curves. Assuming a set of Lennard-Jones parameters, the second virial coefficients are obtained for the N8-N8 complex at a temperature range of 298 to 1000 K. Both the corrected and uncorrected basis set superposition error (BSSE) results are presented confirming the significance of including BSSE corrections.</p>

scholarly journals Temperature dependence of the collision‐induced absorption band of O 2 near 1.27 µm

2021 ◽  
Author(s):  
S. Kassi ◽  
S. Guessoum ◽  
J. C. Acosta Abanto ◽  
H. Tran ◽  
A. Campargue ◽  
...  
Keyword(s):  
Absorption Band ◽  
Temperature Dependence ◽  
Induced Absorption

Intermolecular Potential Function for Ammonia-Lithium Ion Based on Ab-Initio Calculations

1988 ◽  
Vol 43 (2) ◽  
pp. 143-146
Author(s):  
Supot V. Hannongbua ◽  
Sirirat U. Kokpol ◽  
Suchada Kreawsrikul ◽  
Supa Polman ◽  
Bernd M. Rode
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Intermolecular Interaction ◽  
Lithium Ion ◽  
Basis Set ◽  
Intermolecular Potential ◽  
Double Zeta ◽  
Double Zeta Basis ◽  
Lcao Mo

The intermolecular interaction for ammonia-lithium ion has been investigated based on the LCAO-MO-SCF method, with double zeta basis set including polarization. The potential functions were constructed firstly from 50 ammonia configuration. Then 50 additional random configurations were added to test the quality of the function. The results show that even 100 configurations are not enough to obtain convergency, but the quality of the function obtained by well-selected points of the surface is already sufficient for simulation purposes.

Intermolecular Potential Function Including Anisotropie Terms for Ammonia/Cu2+ Based on ab-initio Calculations

1990 ◽  
Vol 45 (11-12) ◽  
pp. 1303-1308
Author(s):  
R. T. Kroemer ◽  
Y. Michopoulos ◽  
B. M. Rode
Keyword(s):  
Charge Transfer ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Potential Function ◽  
Pair Potential ◽  
Basis Set ◽  
Intermolecular Potential ◽  
Transfer Effects

AbstractAn intermolecular pair potential function for Cu2+-NH3 has been derived based on ab-initio calculations with a ECP-DZV basis set. For copper the original ECP-DZV basis set was modified in order to avoid unwanted charge-transfer effects. The final potential function including anisotropic terms was constructed from a total of 679 configurations.

Integrated absorption-band intensity of the valence vibration of the isocyanate group

1972 ◽  
Vol 17 (1) ◽  
pp. 923-925
Author(s):  
N. F. Smirnova ◽  
Yu. I. Mushkin ◽  
A. I. Finkel' Shtein ◽  
B. M. Tsigin
Keyword(s):  
Absorption Band ◽  
Valence Vibration ◽  
Isocyanate Group ◽  
Band Intensity ◽  
Absorption Band Intensity

A Systematic DFT Study of Two Elementary Steps Involving Hydrogen Peroxide and the Hydroxyl Radical in the Fenton Reaction

2018 ◽  
Author(s):  
Danilo Carmona ◽  
David Contreras ◽  
Oscar A. Douglas-Gallardo ◽  
Stefan Vogt-Geisse ◽  
Pablo Jaque ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Hydroxyl Radical ◽  
Ab Initio ◽  
Fenton Reaction ◽  
Basis Set ◽  
Basis Sets ◽  
Dft Methods ◽  
Elementary Steps ◽  
Oxygen Oxygen ◽  
Complete Basis Set

The Fenton reaction plays a central role in many chemical and biological processes and has various applications as e.g. water remediation. The reaction consists of the iron-catalyzed homolytic cleavage of the oxygen-oxygen bond in the hydrogen peroxide molecule and the reduction of the hydroxyl radical. Here, we study these two elementary steps with high-level ab-initio calculations at the complete basis set limit and address the performance of different DFT methods following a specific classification based on the Jacob´s ladder in combination with various Pople's basis sets. Ab-initio calculations at the complete basis set limit are in agreement to experimental reference data and identified a significant contribution of the electron correlation energy to the bond dissociation energy (BDE) of the oxygen-oxygen bond in hydrogen peroxide and the electron affinity (EA) of the hydroxyl radical. The studied DFT methods were able to reproduce the ab-initio reference values, although no functional was particularly better for both reactions. The inclusion of HF exchange in the DFT functionals lead in most cases to larger deviations, which might be related to the poor description of the two reactions by the HF method. Considering the computational cost, DFT methods provide better BDE and EA values than HF and post--HF methods with an almost MP2 or CCSD level of accuracy. However, no systematic general prediction of the error based on the employed functional could be established and no systematic improvement with increasing the size in the Pople's basis set was found, although for BDE values certain systematic basis set dependence was observed. Moreover, the quality of the hydrogen peroxide, hydroxyl radical and hydroxyl anion structures obtained from these functionals was compared to experimental reference data. In general, bond lengths were well reproduced and the error in the angles were between one and two degrees with some systematic trend with the basis sets. From our results we conclude that DFT methods present a computationally less expensive alternative to describe the two elementary steps of the Fenton reaction. However, choice of approximated functionals and basis sets must be carefully done and the provided benchmark allows a systematic validation of the electronic structure method to be employed

Rotational de-excitations of C3H+ (1Σ+) by collision with He: new ab initio potential energy surface and scattering calculations

2020 ◽  
Vol 494 (4) ◽  
pp. 5675-5681 ◽  
Author(s):  
Sanchit Chhabra ◽  
T J Dhilip Kumar
Keyword(s):  
Potential Energy ◽  
Potential Energy Surface ◽  
Ab Initio ◽  
Cross Sections ◽  
Energy Surface ◽  
Molecular Ions ◽  
Basis Set ◽  
Rate Coefficients ◽  
Close Coupling ◽  
Collisional Rate Coefficients

ABSTRACT Molecular ions play an important role in the astrochemistry of interstellar and circumstellar media. C3H+ has been identified in the interstellar medium recently. A new potential energy surface of the C3H+–He van der Waals complex is computed using the ab initio explicitly correlated coupled cluster with the single, double and perturbative triple excitation [CCSD(T)-F12] method and the augmented correlation consistent polarized valence triple zeta (aug-cc-pVTZ) basis set. The potential presents a well of 174.6 cm−1 in linear geometry towards the H end. Calculations of pure rotational excitation cross-sections of C3H+ by He are carried out using the exact quantum mechanical close-coupling approach. Cross-sections for transitions among the rotational levels of C3H+ are computed for energies up to 600 cm−1. The cross-sections are used to obtain the collisional rate coefficients for temperatures T ≤ 100 K. Along with laboratory experiments, the results obtained in this work may be very useful for astrophysical applications to understand hydrocarbon chemistry.

scholarly journals Density Functional Theory and Complete Basis Set Ab Initio Computational Study of Five-, Six-, Seven- and Eight-hydrogen Coordinated Carbon Cations

1999 ◽  
Vol 23 (8) ◽  
pp. 502-503
Author(s):  
Branko S. Jursic
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Computational Study ◽  
Basis Set ◽  
Functional Theory ◽  
Complete Basis ◽  
Complete Basis Set ◽  
High Level

High level ab initio and density functional theory studies are performed on highly protonated methane species.

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