In this study, we analyzed the light absorption by diatomic molecules or colliding atoms in a spectral region dominated by an avoided crossing of adiabatic state levels or crossing of the ...corresponding diabatic state levels. Our attention was focused on the low-resolution spectrum at a higher gas temperature under local thermodynamic equilibrium conditions. The absorption measurements of mixed vapors of potassium (≈80%) and cesium (≈20%) were made in the temperature range of 542–715 K and the infrared spectral range 900–1250 nm. In this area, the main spectral contributions were the broad A 1 Σ ( u ) + ( 0 ( u ) + ) − X 1 Σ ( g ) + ( 0 ( g ) + ) bands of K2, Cs2, and KCs molecules. There was a crossing of A 1 Σ ( u ) + ( 0 ( u ) + ) and b 3 Π ( u ) ( 0 ( u ) + ) state potential curves and the coupling of this state was due to the matrix element ⟨ A 1 Σ ( u ) + ( 0 ( u ) + ) | H s o | b 3 Π ( u ) ( 0 ( u ) + ) ⟩ of the spin–orbit interaction. Using data for relevant electronic potential curves and transition dipole moments existing in the literature, the spectra of the A 1 Σ ( u ) + ( 0 ( u ) + ) − X 1 Σ ( g ) + ( 0 ( g ) + ) molecular bands of K2, Cs2, and KCs molecules were calculated. Full quantum mechanical and semi-quantum coupled channel calculations were done and compared with their non-coherent adiabatic or diabatic approximations. Through the comparison of our theoretical and experimental spectra, we identified all observed spectral features and determined the atoms’ number density and gas temperature.
In this paper we discuss a novel use of a Cs-filled optical cell with micrometric thickness. The cell intrinsically contains an extremely small number of Rb atoms. When heated up to temperatures ...around 350
∘
C, the vapor in the cell consists of: (i) Cs atoms, (ii) an order of magnitude lower concentration
Cs
2
dimers and (iii) a small number of Rb atoms. This mixture is a high density but optically thin alkali vapor layer, and the produced complex ensemble of
Cs
2
diatomic molecules, together with Rubidium and Cesium atoms can be investigated by means of linear/nonlinear spectroscopy. In this work we study the fluorescence and selective reflection spectral profiles of Rb atoms in the presence of high-density Cs atoms considered as a buffer gas for the Rb atoms and Cs dimers. In addition, the Rb hyperfine transition spectrum is used as a precise frequency reference for the measurement of the spectral profile widths and the frequency positions of the experimentally registered spectral lines of
Cs
2
molecules in the spectral region around the Rb
D
2
resonance line.
We present a review on the photoionization bands that can be found in the far ultraviolet part of the spectrum using all sapphire cells in absorption experiments with hot alkali vapor. We describe ...cesium and rubidium dimers which have very pronounced photoionization bands together with bialkali mixtures like KCs and RbCs. We explain the origin of these peculiar bands as special molecular transitions between the ground state of the neutral molecule and exited states of the ionized molecule as a direct ionization process. We also described the diffuse bands as transition from the same ground state molecule to doubly excited molecular state, as an indirect ionization process. Finally, we believe that these two pathways may interfere resulting in a complex structure revealing the observed diffuse bands.
In the paper, several theoretical approaches to the determination of the reduced absorption and emission coefficients under local thermodynamic equilibrium conditions were exposed and discussed. The ...full quantum-mechanical procedure based on the Fourier grid Hamiltonian method was numerically robust but time consuming. In that method, all transitions between the bound, free, and quasi-bound states were treated as bound–bound transitions. The semi-classical method assumed continuous energies of ro-vibrational states, so it did not give the ro-vibrational structure of the molecular bands. That approach neglected the effects of turning points but agreed with the averaged-out quantum-mechanical spectra and it was computer time efficient. In the semi-quantum approximation, summing over the rotational quantum number J was done analytically using the classical Franck–Condon principle and the stationary–phase approximation and its consumption of computer time was lower by a few orders of magnitude than the case of the full quantum-mechanical approach. The approximation described well the vibrational but not the rotational structure of the molecular bands. All the above methods were compared and discussed in the case of a visible and near infrared spectrum of LiHe, Li2, and Cs2 molecules in the high temperature range.
We report the experimental observation of photoionization bands of the KCs molecule in the deep ultraviolet spectral region between 200 and 420 nm. We discuss the origin of observed photoionization ...bands as stemming from the absorption from the ground state of the KCs molecule to the excited states of KCs+ molecule for which we used existing potential curves of the KCs+ molecule. An alternative explanation relies on the absorption from the ground state of the KCs molecule to the doubly excited states of the KCs** molecule, situated above the lowest molecular state of KCs+. The relevant potential curves of KCs** are not known yet, but all those KCs** potential curves are certainly autoionizing. However, these two photoionization pathways may interfere resulting in a special interference structured continuum, which is observed as complex bands.
The time development of the emission spectrum after the ignition of a high pressure cesium lamp has been studied by means of a high resolution digital spectrometer. Many different spectral phenomena ...of atomic, ionic or molecular origin have been followed in time. Xenon spectral lines were detected only within the first few seconds after the ignition. Cesium resonance lines appear almost immediately with xenon spectral lines. The former have an extraordinarily interesting time evolution, especially in their far quasistatic wings. Recombination continua to 6p and 5d levels appear almost immediately as Cs satellite and other molecular bands. Allowed and forbidden atomic spectral lines follow slightly different time evolutions. All these temporal spectral changes of the high pressure cesium lamp could be used for further improvement of this interesting white light source.
•Time development of the cesium high pressure pulsed discharge lamp spectrum.•Observed rise and fall of the xenon lines in first 7s of plasma burning.•Atomic spectral lines and molecular bands observed in emission and in absorption.•The satellite bands in the wings of the resonance lines were followed in time.
KCs Molecular Bands in the Visible Region Beuc, Robert; Pichler, Goran; Sarkisyan, David
Optics and spectroscopy,
11/2020, Letnik:
128, Številka:
11
Journal Article
Recenzirano
We measured light absorption of potassium and cesium mixed vapors at temperatures 360–660°C in the visible spectral region 380–780 nm. By comparison with the absorption of pure potassium or cesium ...vapors, we concluded that the spectral phenomena observed in the mixture peaking at 539 nm, 562 nm (and 700 nm) are new KCs molecular bands. Quantum mechanical calculations of the KCs molecular bands in the visible and near-infrared spectral region were performed using available theoretical potential curves for the KCs molecule. Using these calculations, we identified the three observed molecular bands as 3
1
Π–
X
, 4
1
Σ
+
–
X
, and 1
1
Π–
X
electronic transitions of KCs molecule, respectively.
Photoionization bands of rubidium molecule Rakić, M.; Pichler, G.
Journal of quantitative spectroscopy & radiative transfer,
March 2018, 2018-03-00, Letnik:
208
Journal Article
Recenzirano
•All sapphire cell enabled absorption measurements in deep ultraviolet spectral region at high temperature and high density.•Unusual structured photoionization bands of rubidium dimer have been ...observed overlying smooth atomic photoionization.•Possible interpretation is connected to direct and indirect photoionization of the rubidium molecule.•The results point to the urgent need of appropriate quantum-mechanical calculations of the doubly excited potential curves which are subjected to autoionization.
We studied the absorption spectrum of dense rubidium vapor generated in a T-type sapphire cell with a special emphasis on the structured photoionization continuum observed in the 200–300 nm spectral region. The photoionization spectrum has a continuous atomic contribution with a pronounced Seaton–Cooper minimum at about 250 nm and a molecular photoionization contribution with many broad bands. We discuss the possible origin of the photoionization bands as stemming from the absorption from the ground state of the Rb2 molecule to excited states of Rb2+* and to doubly excited autoionizing states of Rb2** molecule. All these photoionization bands are located above the Rb+ and Rb2+ ionization limits.
Digital interferometry device is described for measuring the thickness variations of the resin composite samples during blue light polymerization. The proposed device enables two types of ...quantitative measurements providing data for: (i) the thickness variations of samples continuously during cure and (ii) the total linear shrinkage of samples. The effects of the initial thermal expansion and the later shrinkage can be clearly resolved for different materials, curing lights, and illumination modes. Simple experimental device is introduced through the results obtained for commercial dental materials.
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