1,721,003 research outputs found
High Resolution Gas Phase IR Spectroscopy Applications
No full textHigh-resolution IR spectroscopy is confined to the study of atoms and molecules in the gas phase at low pressures, where the interaction energy between particles is orders of magnitude lower than in the condensed phases. The intermolecular interactions broaden the energy levels, and, consequently, the spectral lines, preventing the observation of finer details in the spectra. The main applications covered in this chapter are the accurate determination of rotation and rotation-vibration molecular energies; the determination of the molecular geometry of simple molecules; the evaluation of force field and of the vibration- and rotation-vibration interactions; the measurement of pressure broadening and pressure shift of the spectral lines; the determination of electric dipole moments via laser-Stark spectroscopy; the studies of intramolecular dynamics; the calculation of rate constants, equilibrium constants and other thermodynamic data; the evaluation of relaxation times
Assignment of the 283-nm absorption spectrum of 4-azabenzimidazole as π*-π by rotational band contour analysis
No full textThe 000 band of the 283-nm system of 4-azabenzimidazole has been analyzed by computer simulation of its rotational contour to establish the character of the S1-S0 electronic transition. The 000 band has been shown to be an A B hybrid with an intensity ratio B A = 0.15, so the S1-S0 system can be assigned as A ̃1A′(π*-π)- X ̃1A′. Since the 000 band of the 289-nm system for 7-azaindole has also been shown to be of the same type (K. H. Hassan and J. M. Hollas, J. Mol. Spectrosc. 138, 398-412 (1989)), we conclude that the addition of an extra nitrogen in 4-azabenzimidazole does not change the nature of the first singlet electronic transition. © 1991
High Resolution Gas Phase IR Spectroscopy Applications
No full textHigh-resolution IR spectroscopy is confined to the study of atoms and molecules in the gas phase at low pressures, where the interaction energy between particles is orders of magnitude lower than in the condensed phases. The intermolecular interactions broaden the energy levels, and, consequently, the spectral lines, preventing the observation of finer details in the spectra. The main applications covered in this chapter are the accurate determination of rotation and rotation-vibration molecular energies; the determination of the molecular geometry of simple molecules; the evaluation of force field and of the vibration- and rotation-vibration interactions; the measurement of pressure broadening and pressure shift of the spectral lines; the determination of electric dipole moments via laser-Stark spectroscopy; the studies of intramolecular dynamics; the calculation of rate constants, equilibrium constants and other thermodynamic data; the evaluation of relaxation times. © 1999 Elsevier Ltd All rights reserved
The harmonic vibrational frequencies and the geometry of the 12C6H6
No full textThe harmonic frequencies ωest of 12C6H6 calculated by combining the anharmonic constants from a DFT quartic force field with the experimental fundamentals, are compared with harmonic frequencies, ωcalc, obtained with different theoretical methods. One set of ωcalc was derived by Martin, Taylor and Lee by ab initio CCSD(T) theory, the others have been calculated by us by means of the density funcional theory DFT with B3LYP, B3PW91, B3P86 and mPW1PW hybrid functionals. The mean absolute deviation between ab initio ωcalc and ωest is 6.8 cm-1 while between DFT ωcalc and ωest is between 8.6 and 10.5 cm-1. Moreover the DFT ωcalc show a small systematic underestimation of the CH stretching vibrations. © 2001 Elsevier Science B.V
The v6, v7, v8 and v19 gas phase fundamental frequencies of 12C6H6
No full textThe fundamental wavenumbers v6, v7, v8 and v19 of gas phase benzene have been accurately determined from combination and difference bands present in the infrared spectrum. The anharmonic contribution to the vibrational energy was estimated by means of some anharmonic constants calculated by ab initio methods by Handy et al. [J. Chem. Phys. 97 (1992) 4233]. The fundamentals were checked by comparison with the overtones present in the Raman spectrum determined by Eppinger et al. [J. Mol. Struct. 266 (1992) 389]. © 1997 Elsevier Science B.V
Assignment of the S1-S0 Electronic Absorption Spectra of 1H-Benzotriazole and of 1,2,4-Triazolo[1,5-a]Pyrimidine as π*-π by Rotational Band Contour Analysis
No full textThe 000 bands in the S1-S0 electronic absorption systems of lH-benzotriazole at 286 nm and of 1,2,4-triazolo[l,5-a]pyrimidine at 315 nm have been analyzed by computer simulation of their rotational contours. The results have shown that the benzotriazole hand is an almost pure type-B band, while in the case of 1,2,4-triazolo[l,5-a] pyrimidine it is a pure type-A band, so each S1-S0 electronic system is assigned as Ã1A′(ππ*)-X̃1A′. In both of these molecules, the transition moment is in the molecular plane, almost parallel to the b-inertial axis in benzotriazole. while it is parallel to the a-inertial axis in 1,2,4-triazolo[1,5-a]pyrimidine. Since the S1-S0 transitions in the indole derivatives previously analyzed were shown to be π*-π, it seems likely that the nature of the S1-S0 electronic transition is the same in all the molecules of this kind. © 1993 Academic Press, Inc
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
