Dunham Parameters Research Articles

Laser spectroscopy of the AO + −X 1Σ + system of TlCl

The AO + −X 1Σ + transition of TlCl is investigated by excitation spectroscopy and direct absorption detection with frequency-doubled laser radiation. From the resolved fine structure of all natural isotope combinations of TlCl, Dunham parameters, Born—Oppenheimer correction parameters and field-shift parameters are determined. The lower vibrational levels of AO + show complete rotational structure, while the upper levels v′ = 4, 5, 6 for the excitation spectra exhibit typical fragmentary bands as expected for predissociation where the rate of predissociation can become much larger than the rate of radiational decay. With direct absorption technique, these fragmentary bands are recorded as complete bands, containing broadened rotational transitions with half widths of more than 30 GHz. The qualitative interpretation of the predissociation is compared with the results of photofragment spectroscopy.

Molecular-beam-laser studies of the states X1Σ+ and A0+ of PbS

Abstract By using a molecular-beam apparatus, laser excitation spectra and microwave-optical double-resonance spectra were observed on the electronic states X 1 Σ + and A0 + of PbS. For the microwave spectra a resolution up to 10 kHz was achieved and microwave two-photon transitions could be detected. All information was combined into single fitting routine including data from other sources. Besides the usual Dunham parameters the fit model takes account of the breakdown of the Born-Oppenheimer approximation and the isotopic field shift. From the field shift of the electronic energy, the vibrational motion and the rotational motion the electron density as a function of the internuclear distance at the Pb nucleus is derived, which allows a more detailed discussion of the electronic structure of the molecule in combination with future quantum-chemical calculations. Additionally it is shown that the variation of the electron density along the vibrational motion at low vibrational levels can be as large as the variation for the electronic transition A0 + -X 1 Σ + in the case of PbS. The magnetic hyperfine structure of 207 Pb is resolved in a molecule for the first time. The coupling parameter of PbS is compared with that of the isovalent molecule TlCl.

The lowest rotational transition of several isotopic forms of KrD+

The J=0–1 absorption line of KrD+ has been observed for all six stable krypton isotopes in a dc glow discharge in Kr–D2 mixtures. For 83KrD+ the quadrupole coupling constant [eQq=549.1(5) MHz] and nuclear magnetic coupling constant [CN=−0.022(2) MHz] were determined. By combining the new microwave data for KrD+ with very precise published Dunham constants for KrH+ from Johns’ high resolution infrared spectral data, the mass independent Dunham parameters U01, ΔH01, and ΔKr01 were deduced. Precise Doppler shift measurements indicated a small drift velocity in the magnetic field enhanced, abnormal discharge in the direction opposite to that naively expected from the electrode polarity.

Doppler free polarization spectroscopy of SrCl: The B 2Σ+–X 2Σ+ system

A rotation-vibration analysis of the SrCl B 2Σ+–X 2Σ+ system is reported. Large parts of the (0,0), (1,1), and (2,2) bands were recorded using Doppler free polarization spectroscopy and microwave labeling was employed in order to simplify the complex spectra. The optical data were combined with the results of independent microwave measurements of the X 2Σ+ state in a weighted least squares fit. The heads of four Δv=+1 bands were measured for the vibrational analysis. The main Dunham parameters (2σ error in parentheses) for the Sr35Cl B 2Σ+ state are Y10=0.103 110 64(78) cm−1, Y11=−0.473 94(70)×10−3 cm−1, Y10=307.056(19) cm−1, and Y20=−1.0156(34) cm−1; Te=15 722.8176(14) cm−1.

Effects of unresolved hyperfine structure in the microwave rotational spectra of the 2Σ-radicals CaBr and CaCl

The microwave rotational spectra of gaseous CaBr and CaCl have been measured in the 90-107 GHz and 270-290 GHz region. Precise values of the Dunham parameters Y 01, Y 11, Y 2, and Y 02 are given for the isotopic species Ca 79Br, Ca 81Br, Ca 35Cl and Ca 37Cl. It is shown that effects of unresolved hyperfine structure may cause considerable systematic errors in the determination of the spin-rotation constant Ψ even if the hyperfine structure splitting is so small that not even inhomo- geneous line broadening can be observed in the spectrum. If the hyperfine structure parameters are not known from other sources these effects will limit the accuracy for the determination of Ψ from microwave spectra.

Diatomic molecules as perturbed Morse oscillators. V. Centrifugal distortion

The perturbed-Morse-oscillator model is extended to include computation of Dunham parameters Yjk for k⩽3 and for arbitrary j. A computer code incorporating this extension is used to compute energy eigenvalues Ev,J for the ground state of CO for v⩽28 and for J⩽160. Results are compared with eigenvalues obtained by other methods and analyzed to show the various problems of convergence encountered.