THE EXCITATION OF BAND SPECTRA—ROTATIONAL STRUCTURE

1935 ◽  
Vol 12 (1) ◽  
pp. 6-13 ◽  
Author(s):  
G. O. Langstroth
Keyword(s):  
Excitation Energy ◽  
Electronic Configuration ◽  
Rotational Structure ◽  
Molecular Field ◽  
Exciting Electron ◽  
Band Spectra

An examination of the intensity contours of three second positive nitrogen bands excited by electrons of 14, 15, 16 and 18 electron volts energy, indicates that the contours change in shape as the energy of the exciting electrons is varied. These results and their relation to those of other investigators can be understood if there is a definite probability that an impinging electron will excite the electronic configuration of a molecule and then interact with the rotation before escaping from the molecular field. As might be expected, this probability is appreciable only when the energy of the exciting electron is nearly equal to the excitation energy.

scholarly journals Quantum analysis of the rotational structure of the first positive bands of nitrogen (N 2 )

1932 ◽  
Vol 136 (829) ◽  
pp. 114-144 ◽  
Keyword(s):  
Electronic Configuration ◽  
Selective Excitation ◽  
Nitrogen Molecule ◽  
Rotational Structure ◽  
Positive System ◽  
Initial State ◽  
Final State ◽  
Active Nitrogen ◽  
Quantum Analysis ◽  
Vibrational Levels

The greenish-yellow afterglow of active nitrogen was first described, by Lewis. Two decades have passed since Fowler and Strutt showed that this afterglow was due to a selective excitation of a few green, yellow and red bands belonging to the first positive system of the nitrogen molecule (N 2 ). Recent work on active nitrogen indicates that the selective excitation is due to metastable nitrogen atoms giving up their energy to metastable nitrogen molecules in state A, the final state of the first positive bands, thus leading to the selective excitation of certain specific vibrational levels in state B, the initial state of the first positive bands. The molecule then returns to state A, at the same time emitting the bands which constitute the afterglow. From the rotational analysis of the second positive nitrogen bands by Lindau, and Hulthèn and Johansson, it is known that state B corresponds to a 3 II state, the second positive bands having their final state in common with the initial state of the first positive bands. No definite information has been found concerning the electronic configuration of the nitrogen molecule which gives rise to state A. This can be obtained by making a detailed analysis of the rotational structure of the first positive nitrogen bands.

scholarly journals On the fine structure of the band-spectra of sodium, potassium and sodium-potassium vapours

1924 ◽  
Vol 106 (738) ◽  
pp. 400-415 ◽  
Keyword(s):  
Fine Structure ◽  
Quantum Theory ◽  
Electronic Configuration ◽  
Normal Band ◽  
Final States ◽  
Sodium Potassium ◽  
Complete Group ◽  
Centre Of Gravity ◽  
Wave Numbers ◽  
Band Spectra

It has become of importance to analyse the fine structure of band spectra since it has been shown that, by the application of the quantum theory, certain information can be obtained concerning the molecules which give rise to these spectra. It is assumed that the fine lines of which these bands are composes are due to simultaneous changes in the electronic configuration of the molecule in the oscillation of the nuclei along the line joining them, and in the rotation of the molecule about its centre of gravity. It can then be shown that the frequencies of the lines in a group of bands are given by ν = ν e + nν n + ( h /8 π 2 I´ ± mh /4 π 2 I´) + m 2 h /8 π 2 (1/I´ – 1/I) where n and m are integers. In this formula ν e is a frequency depending on the change in electronic configuration; to each value of ν e characteristic of the molecule corresponds a complete group of bands. ν a depends on the oscillation of the nuclei, and the remaining terms depend on the rotation of the molecule, I´ and I being the moments of inertia in the initial and final states. This shows that the wave-numbers of the fine lines of a single band, when plotted against the series of integers, fall on the three parabolas Q( m ) = A + C m 2 P( m ) = A + B – 2B m + C m 2 R( m ) = A + B + 2B m + C m 2 where A = ν e + n ν n / c , B = h /8 π 2 c I´ C = h /8 π 2 c (1/I´ – 1/I). When this notation, which is that of Sommerfeld, is used, all three series of a normal band are given by three constants.

EMISSION BAND SPECTRA OF NITROGEN: A STUDY OF SOME SINGLET SYSTEMS

1957 ◽  
Vol 35 (2) ◽  
pp. 216-234 ◽  
Author(s):  
Alf Lofthus
Keyword(s):  
Electronic Structure ◽  
High Resolution ◽  
Emission Band ◽  
Rotational Structure ◽  
Electron Configuration ◽  
Excitation Energies ◽  
Local Perturbations ◽  
Singlet States ◽  
Band Spectra ◽  
Vibrational Constants

Ten bands of Gaydon's and Herman's singlet systems and eight new bands have been photographed under high resolution and analyzed in detail. Two of the new transitions were shown to be [Formula: see text], the upper state being in one case identical with Watson's and Koontz's state g, and one new transition to be 1Δg—ω1Δu in type. It is proposed that the new state 1Δg has the same electron configuration as the [Formula: see text] state. Two bands in the red and one band in the ultraviolet could not be assigned with certainty. Local perturbations in the [Formula: see text] state were observed and shown to be caused by the ν = 1 level of the [Formula: see text] state. Observed pecularities in the rotational structure of most of the upper states are proposed to be indicative of a transition from case b′ to d′ coupling. In some cases pronounced decreases in branch intensities were observed, indicating predissociations probably caused by "forbidden" intercombination processes. Identification of the electronic structure of the higher singlet states in terms of Rydberg orbitals is discussed. Rotational and vibrational constants and excitation energies are presented.

scholarly journals Interpretation of the spectra of CaF and SrF

1931 ◽  
Vol 133 (821) ◽  
pp. 336-350 ◽  
Keyword(s):  
Alkaline Earth ◽  
Isotope Effects ◽  
Indirect Evidence ◽  
Ultra Violet ◽  
Rotational Structure ◽  
Quantum Numbers ◽  
Combination Principle ◽  
Band Spectra ◽  
The Individual ◽  
Concave Grating

The structure of the band spectra of the diatomic alkaline earth fluorides has been considered in the light of the quantum theory by Mecke, Jevons, Johnson, and Jenkins. Because of the closeness of the rotational structure it has proved impossible to obtain sufficient resolution for the application of the combination principle to the individual band lines except for BeF, which molecule has the smallest moment of inertia (Jenkins, loc . cit .). With the heavier molecules, assignments of vibrational quantum numbers were made from the positions and intensities of the band heads, and designations of the electronic terms were given, based on the evident similarity of certain band systems in this group of molecules. The 2 Π→ 2 Σ system, which lies in the ultra-violet for BeF and MgF, and in the visible for CaF, SrF and BaF, was shown in the case of BeF to possess the expected rotational structure. The system designated 2 Σ→ 2 Σ by Johnson is known only in CaF, SrF and BaF, and has a slightly higher frequency than 2 Π→ 2 Σ. In the course of a search for isotope effects in the spectra of CaF and SrF have obtained plates with the 21-foot concave grating showing the two systems mentioned above in both emission and absorption. For the absorption the method of Walters and Barratt was used. Although the study of these plates gave evidence of isotopes only in the case of SrF, certain observations on the modifications in structure between emission and absorption are important for the interpretation of the rotational structure of the bands of both molecules, a question which apparently can only be cleared up by indirect evidence of this kind.

HIGH PRESSURE OXYGEN A-BAND SPECTRA

2015 ◽  
Author(s):  
Brian Drouin ◽  
Jiajun Hoo ◽  
V. Devi ◽  
D. Benner ◽  
David Robichaud ◽  
...  
Keyword(s):  
High Pressure ◽  
Pressure Oxygen ◽  
High Pressure Oxygen ◽  
Band Spectra

Thymine Dimerization Induced by Oxidative DNA Lesions and Epigenetic Intermediates via Triplet-Triplet Energy Transfer

2020 ◽  
Author(s):  
Mauricio Lineros-Rosa ◽  
Antonio Francés-Monerris ◽  
Antonio Monari ◽  
Miguel Angél Miranda ◽  
Virginie Lhiaubet-Vallet
Keyword(s):  
Energy Transfer ◽  
Excitation Energy ◽  
Transient Absorption ◽  
Theoretical Calculations ◽  
Dna Lesions ◽  
Transient Absorption Spectroscopy ◽  
Triplet Energy ◽  
Pyrimidine Dimers ◽  
Triplet Energy Transfer ◽  
Dna Nucleobases

Interaction of nucleic acids with light is a scientific question of paramount relevance not only in the understanding of life functioning and evolution, but also in the insurgence of diseases such as malignant skin cancer and in the development of biomarkers and novel light-assisted therapeutic tools. This work shows that the UVA portion of sunlight, not absorbed by canonical DNA nucleobases, can be absorbed by 5-formyluracil (ForU) and 5-formylcytosine (ForC), two ubiquitous oxidative lesions and epigenetic intermediates present in living beings in natural conditions. We measure the strong propensity of these molecules to populate triplet excited states able to transfer the excitation energy to thymine-thymine dyads, inducing the formation of the highly toxic and mutagenic cyclobutane pyrimidine dimers (CPDs). By using steady-state and transient absorption spectroscopy, NMR, HPLC, and theoretical calculations, we quantify the differences in the triplet-triplet energy transfer mediated by ForU and ForC, revealing that the former is much more efficient in delivering the excitation energy and producing the CPD photoproduct. Although significantly slower than ForU, ForC is also able to harm DNA nucleobases and therefore this process has to be taken into account as a viable photosensitization mechanism. The present findings evidence a rich photochemistry crucial to understand DNA photodamage and of potential use in the development of biomarkers and non-conventional photodynamic therapy agents.

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