Diatomic molecule, orbitals ionization energy

Atomic spectra, which historically contributed extensively to the development of the theory of the structure of the atom and led 10 the discovery of the electron and nuclear spin, provide a method of measuring ionization potentials, a method for rapid and sensitive qualitative and quantitative analysis, and data for the determination of the dissociation energy of a diatomic molecule. Information about the type of coupling of electron spin and orbital momenta in the atom can be obtained with an applied magnetic field. Atomic spectra may be used to obtain information about certain regions of interstellar space from the microwave frequency emission by hydrogen and to examine discharges in thermonuclear reactions. 

Existing basis sets perform poorly for transition metals, the major problem being the D shell. An improved 6-3IG basis set (called m6-31G) for first-row transition metals has been proposed, with new orbital exponents and contraction coefficients for the D shell, which performs uniformly well across the entire first-row transition metal series from Sc to Cu. The quality of the new basis set is demonstrated for accurate prediction of ionization energies and bond dissociation energies, as well as structural parameters and harmonic vibrational frequencies of diatomic and polyatomic molecules. Because of its uniformly good performance for all first row transition metals, this m6-31G basis set, and its derivatives, e.g., m6-31G, is recommended over the original 6-3IG set or its derivatives. We await applications to shielding calculations. 

Unlike the stable molecule N2O, the sulfur analogue N2S decomposes above 160 K. In the vapour phase N2S has been detected by high-resolution mass spectrometry. The IR spectrum is dominated by a very strong band at 2040 cm [v(NN)]. The first ionization potential has been determined by photoelectron spectroscopy to be 10.6 eV. " These data indicate that N2S resembles diazomethane, CH2N2, rather than N2O. It decomposes to give N2 and diatomic sulfur, S2, and, hence, elemental sulfur, rather than monoatomic sulfur. Ab initio molecular orbital calculations of bond lengths and bond energies for linear N2S indicate that the resonance structure N =N -S is dominant. 

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