dorsal/arxiv
View SchemaBenchmark ab initio thermochemistry of the isomers of diimide, N_2H_2, using accurate computed structures and anharmonic force fields
| Authors | Jan M. L. Martin, Peter R. Taylor |
|---|---|
| Categories | |
| ArXiv ID | physics/9808014 |
| URL | https://arxiv.org/abs/physics/9808014 |
| DOI | 10.1080/002689799165530 |
| Journal | Molecular Physics 96, 681-692 (1999) [B. Liu memorial issue] |
Abstract
A benchmark ab initio study on the thermochemistry of the trans-HNNH, cis-HNNH, and H$_2$NN isomers of diazene has been carried out using the CCSD(T) coupled cluster method, basis sets as large as $[7s6p5d4f3g2h/5s4p3d2f1g]$, and extrapolations towards the 1-particle basis set limit. The effects on inner-shell correlation and of anharmonicity in the zero-point energy were taken into account: accurate geometries and anharmonic force fields were thus obtained as by-products. Our best computed $\Delta H^\circ_{f,0}$ for trans-HNNH, 49.2 \pm 0.3 kcal/mol, is in very good agreement with a recent experimental lower limit of 48.8 \pm 0.5 kcal/mol. CCSD(T) basis set limit values for the isomerization energies at 0 K are 5.2 \pm 0.2 kcal/mol (cis-trans) and 24.1 \pm 0.2 kcal/mol (iso-trans). Our best computed geometry for trans-HNNH, $r_e$(NN)=1.2468 \AA, $r_e$(NH)=1.0283 \AA, and $\theta_e$=106.17$^\circ$, reproduces the precisely known ground-state rotational constants of trans-HNNH to within better than 0.1 %. The rotation-vibration spectra of both cis-HNNH and H$_2$NN are dominated by very strong Coriolis and Fermi resonances. In addition, the NH stretches in H$_2$NN are so strongly anharmonic that vibrational perturbation theory breaks down, and the molecule appears to be an excellent test case for variational treatments of the vibrational Schr\"odinger equation.
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"abstract": "A benchmark ab initio study on the thermochemistry of the trans-HNNH,\ncis-HNNH, and H$_2$NN isomers of diazene has been carried out using the CCSD(T)\ncoupled cluster method, basis sets as large as $[7s6p5d4f3g2h/5s4p3d2f1g]$, and\nextrapolations towards the 1-particle basis set limit. The effects on\ninner-shell correlation and of anharmonicity in the zero-point energy were\ntaken into account: accurate geometries and anharmonic force fields were thus\nobtained as by-products. Our best computed $\\Delta H^\\circ_{f,0}$ for\ntrans-HNNH, 49.2 \\pm 0.3 kcal/mol, is in very good agreement with a recent\nexperimental lower limit of 48.8 \\pm 0.5 kcal/mol. CCSD(T) basis set limit\nvalues for the isomerization energies at 0 K are 5.2 \\pm 0.2 kcal/mol\n(cis-trans) and 24.1 \\pm 0.2 kcal/mol (iso-trans). Our best computed geometry\nfor trans-HNNH, $r_e$(NN)=1.2468 \\AA, $r_e$(NH)=1.0283 \\AA, and\n$\\theta_e$=106.17$^\\circ$, reproduces the precisely known ground-state\nrotational constants of trans-HNNH to within better than 0.1 %. The\nrotation-vibration spectra of both cis-HNNH and H$_2$NN are dominated by very\nstrong Coriolis and Fermi resonances. In addition, the NH stretches in H$_2$NN\nare so strongly anharmonic that vibrational perturbation theory breaks down,\nand the molecule appears to be an excellent test case for variational\ntreatments of the vibrational Schr\\\"odinger equation.",
"arxiv_id": "physics/9808014",
"authors": [
"Jan M. L. Martin",
"Peter R. Taylor"
],
"categories": [
"physics.chem-ph"
],
"doi": "10.1080/002689799165530",
"journal_ref": "Molecular Physics 96, 681-692 (1999) [B. Liu memorial issue]",
"title": "Benchmark ab initio thermochemistry of the isomers of diimide, N_2H_2, using accurate computed structures and anharmonic force fields",
"url": "https://arxiv.org/abs/physics/9808014"
},
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