Journal article
Benchmark ab initio thermochemistry of the isomers of diimide, N2H2, using accurate computed structures and anharmonic force fields
Molecular Physics, Vol.96(4), pp.681-692
Feb/1999
Abstract
A benchmark ab initio study on the thermochemistry of the trans-HNNH, cis-HNNH, and H2NN isomers of diazene has been carried out using the CCSD(T) coupled cluster method, basis sets as large as [7s6p5d4f3g2h/5s4p3d2flg], and extrapolations towards the I-particle basis set limit. The effects on inner shell correlation and of anharmonicity in the zero-point energy were taken into account: thus accurate geometries and anharmonic force fields were obtained as by-products. The best computed Delta H(f0)degrees for trans-HNNH, 49.2 +/- 0.3 kcal mol(-1), is in very good agreement with a recent experimental lower limit of 48.8 +/- 0.5 kcal mol(-1) CCSD(T) basis set limit values for the isomerization energies at 0 K are 5.2 +/- 0.2 kcal mol(-1) (cis-trans) and 24.1 +/- 0.2 kcal mol(-1) (iso-trans). Our best computed geometry for trans- HNNH, r(e)(NN)= 1.2468 Angstrom, r(e)(NH) = 1.0283 Angstrom, and theta(e) = 106.17 degrees, 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 H2NN are dominated by very strong Coriolis and Fermi resonances. In addition, the NH stretches in H2NN 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 Schrodinger equation.
Details
- Title
- Benchmark ab initio thermochemistry of the isomers of diimide, N2H2, using accurate computed structures and anharmonic force fields
- Creators
- JML Martin (null) - The Weizmann Institute of SciencePR Taylor (null)
- Resource Type
- Journal article
- Publication Details
- Molecular Physics, Vol.96(4), pp.681-692; Feb/1999
- Number of pages
- 12
- Language
- English
- DOI
- https://doi.org/10.1080/00268979909483004
- Grant note
- J. M. is a Yigal Allon Fellow, the incumbent of the Helen and Milton A. Kimmelman Career Development Chair (Weizmann Institute), and an Honorary Research Associate ('Onderzoeksleider in eremandaat') of the National Science Foundation of Belgium (NFWO/FNRS). This research was supported by the National Science Foundation (USA) through Cooperative Agreement DACI-9619020 and by Grant No. CHE-9700627 (PRT), and by a grant of computer time from SDSC.
- Record Identifier
- 993262728403596
Metrics
1 Record Views