Transition intensities energy accuracy

A general framework has been set to compute thermodynamic properties, vibrational energies, and transition intensities from the vibrational ground state to fundamentals, overtones, and combination bands [72, 214, 229- 231] fulfilling the accuracy (for frequencies) and interpretability (for intensities) requirements, and allowing to simulate very accurate vibrational spectra of single molecules or mixtures of several species or conformers, which can be directly compared with experimental data [89]. 

The planned measurements will be able to accumulate an intensity of more than 10000 events per transition enabling a determination of the transition energy with a statistical accuracy of better than 3 meV. For the 3-1 and 4-1 transitions in pionic hydrogen pionic oxygen and carbon transitions adjacent in energy are available as calibration lines, thus avoiding the systematic errors in the former experiment. In a first step the experiment will establish a result for the shift independent of pressure. In order to achieve this the position of the 3-1 and 4-1 lines will be measured as a function of pressure in the region between... 

In the present paper, we show that it is possible to calculate both vibrational and electronic transitions of H2SO4 with an accuracy that is useful in atmospheric simulations. We calculate the absorption cross sections from the infrared to the vacuum UV region. In Section 2 we describe the vibrational local mode model used to calculate OH-stretching and SOH-bending vibrational transitions as well as their combinations and overtones [42-44]. This model provides frequencies and intensities of the dominant vibrational transitions from the infrared to the visible region. In Section 3 we present vertical excitation energies and oscillator strengths of the electronic transitions calculated with coupled cluster response theory. These coupled cluster calculations provide us with an accurate estimate of the lowest... 

Limitations to the spectroscopic measurement of the temperatures from line intensities lie in possible deviations from ideal thermodynamic behavior in real radiation sources, but also in the poor accuracy of transition probabilities. They can be calculated from quantum mechanics, and have been determined and compiled by Corliss and Bozman at NIST [10] from measurements using a copper dc arc. These tables contain line energy levels, transition probabilities and the so-called oscillator strengths for ca. 25000 lines between 200 and 900 nm for 112 spectra of 70 elements. Between the oscillator strength f (being 0.01-0.1 for non-resonance and nearer to 1 for resonance lines) there is the relationship [11] ... 

Since both the splitting energies and intensities of excitonic transitions can be established experimentally with a high degree of accuracy, theoretical determination of those quantities is important. 

In previous calculations [235, 237] only the 7F6—>5D4 transition channel was considered, but other wavefunctions are admixed (to small extents) into 7F6 and 5D4, so that other channels 7F6—>7F4, 5F4, 3F4 5G6—>5D4, 7F4, 5F4, 3F4 and 7F4—>5D4, 7F4, 5F4, 3F4 may contribute to the intensity. In fact, the dominant contributions are found to be 7F4—>7F4 and 7F6—>7F4, and not the nominal 7F6—>5D4. As mentioned above for the vibronic intensity calculations, the accuracy of the wavefunctions and energies employed is the key factor in obtaining agreement between theory and calculation. 

For complexes with relatively simple electronic structures (e.g. d1 and d9 species), DFT Xa methods have demonstrated useful accuracy for both d-d and CT features, especially when Slater s transition state formalism [15] is used. The d-d and CT transition energies of chlorocuprates (II) have been well studied [113-115] and the observed transition energies can be reproduced to about 1000 cm "1 or better. MSXa calculations [114] also predict relative intensities in reasonable agreement with experiment. 

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