M W D Mansfield

The cavity ring-down absorption spectrum of the S0→T1 and S0→S1 transition of jet-cooled 4-H-1-benzopyrane-4-thione

Abstract The very sensitive cavity ring-down method has been applied to the measurement of the absorption of 4-H-1-benzopyrane-4-thione (BPT) in a supersonic jet in the wavelength region of the S0→T1 and S0→S1 transition between 15800 and 16650 cm−1. The absorption energies of vibronic states corroborate previous assignments in the multi-photon excitation and S0→T1 phosphorescence excitation spectra of jet-cooled BPT. The symmetry forbidden 0,0 transition, S0,0→S1,0 at 16522 cm−1, was found to be 7.5 times weaker than the absorption transition to the triplet origin, S0,0→T1z,0.

The identification of 'optically forbidden' autoionising levels of zinc

In a recent study of the ejected-electron spectrum of zinc vapour following excitation by electron impact (see Back et al. (1981)), a number of lines were reported which could not be attributed to the autoionisation of known Zn I levels, viz. levels which had been excited in photoabsorption experiments. Most of the new lines are identified by comparison with ab initio Zn I calculations by the author. In the course of the analysis some anomalies encountered in previous comparisons between theory and photoabsorption measurements are explained. In particular the energy adopted for the Zn I 4p5s 1P1 level is changed significantly. Four Zn I configurations, 3d94s24p, 3d104p5s, 3d104p5p and 3d104p4d are analysed in detail.

The autoionising spectra of cadmium

Extensive multiconfigurational calculations of Cd I and Cd II autoionising levels are reported and are used to analyse in detail the ejected electron spectra of cadmium as reported by Pejcev et al. (1977). Earlier analyses of the Cd I photoabsorption spectrum in the vacuum ultraviolet are generally confirmed and often extended.

The phosphorescence excitation spectrum of jet-cooled 4-H-1-benzopyrane-4-thione

Abstract The phosphorescence excitation spectrum of isolated 4-H-1-benzopyrane-4-thione molecules (BPT) in a pulsed supersonic jet was investigated by direct excitation of the first excited triplet state, S 0 → T 1 . The electronic origin at 15828 cm −1 is assigned to the transition S 0,0 → T 1z,0 , the transition S 0,0 ⇌ T 1(xy),0 is too weak to be detected with this method. The triplet lifetime τ T 1z,0 ≈ 11 μ s is compatible with extrapolated values for BPT in dilute solutions. Vibronic transitions S 0,0 → T 1z,v were measured up to ∼ 1940 cm −1 above the origin; the vibrational structure of T 1 was compared with the vibrational structure of S 2 . S 0,0 → S 1,v absorptions were not observed in the laser-induced phosphorescence experiment. Hot bands were observed under specific experimental conditions.

A multiconfigurational analysis of the 3d spectra of Rb I and Sr I

The results of HXR calculations of the 3d subshell absorption spectra of Rb I and Sr I are presented. Both the transition energies and their intensities are compared with experiment and the resulting assignments of the experimental peaks are discussed in relation to those obtained by self-consistent field calculations and by the Z+1 approximation. The limitations in the applicability of the Z+1 model in cases where strong s-d mixing is induced by wavefunction collapse are indicated.

The resonance-enhanced multiphoton excitation spectrum of jet-cooled 4-H-1-benzopyrene-4-thione

Abstract The multiphoton (one-colour) excitation spectrum of jet-cooled 4-H-1-benzopyrane-4-thione (BPT) is investigated in the wavelength region from 570 to 640 nm. The emission from BPT after multiphoton excitation was detected in two wide ranges in the blue (≈ 400–500 nm) and the near UV (≈ 250–400 nm). Resonance-enhanced excitation via the first excited triplet state S 0 → T 1 → ψ ′ S,T is observed. The time dependence of the luminescence shows two components: (i) a fast decay component ( τ f 2 → S 0 fluorescence after two-photon excitation; (ii) a slow component ( τ s ≈ 2 μ s) which may be attributed to the emission from a photofragment (CS ∗ ), efficiently created in a metastable triplet state by a four-photon absorption.

The critical double-well in Ba+: many-body approach by the g-Hartree method

A novel many-body approach, developed recently for atoms (the g-Hartree method), has been applied to the critical double-well problem in Ba+. A significant improvement over earlier ab initio approaches is demonstrated and correlations are shown to have a large effect. A correct choice of g leads to simultaneous agreement between theory and experiment for three different classes of data, namely, quantum defects, intensity variation and the spin-orbit splitting.

Multi-photon UV photolysis of gaseous polycyclic aromatic hydrocarbons: Extinction spectra and dynamics

The extinction spectra of static naphthalene and static biphenylene vapor, each buffered with a noble gas at room temperature, were measured as a function of time in the region between 390 and 850 nm after UV multi-photon laser photolysis at 308 nm. Employing incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS), the spectra were found to be unstructured with a general lack of isolated features suggesting that the extinction was not solely based on absorption but was in fact dominated by scattering from particles formed in the photolysis of the respective polycyclic aromatic hydrocarbon. Following UV multi-photon photolysis, the extinction dynamics of the static (unstirred) closed gas-phase system exhibits extraordinary quasi-periodic and complex oscillations with periods ranging from seconds to many minutes, persisting for up to several hours. Depending on buffer gas type and pressure, several types of dynamical responses could be generated (classified as types I, II, and III). They were studied as a function of temperature and chamber volume for different experimental conditions and possible explanations for the oscillations are discussed. A conclusive model for the observed phenomena has not been established. However, a number of key hypotheses have made based on the measurements in this publication: (a) Following the multi-photon UV photolysis of naphthalene (or biphenylene), particles are formed on a timescale not observable using IBBCEAS. (b) The observed temporal behavior cannot be described on basis of a chemical reaction scheme alone. (c) The pressure dependence of the systems responses is due to transport phenomena of particles in the chamber. (d) The size distribution and the refractive indices of particles are time dependent and evolve on a timescale of minutes to hours. The rate of particle coagulation, involving coalescent growth and particle agglomeration, affects the observed oscillations. (e) The walls of the chamber act as a sink. The wall conditions (which could not be quantitatively characterized) have a profound influence on the dynamics of the system and on its slow return to an equilibrium state.

Subvalence s-subshell excitation in K, Rb and Cs atoms

Photoabsorption by the subvalence s subshells of the heavy alkali elements K, Rb and Cs is reported. Observations are compared with ab initio calculations and it is shown that mixing of s-subshell excited configurations with doubly excited p-subshell configurations must be included to obtain a satisfactory explanation of the observed spectra.

Theoretical study of photoionization of the isoelectronic sequence Rb+, Sr2+, and Y3+

The photoionization cross sections for the 4p shell of ions of the Kr isoelectronic sequence Rb+, Sr2+, and Y3+ are calculated. The configuration interaction theory and the perturbation theory are used to describe the many-electron effects. The relativistic effects are taken into account in the Pauli-Fock approximation. The calculated resonance structure of photoionization cross sections for the 4p shell in the region below the 4s threshold associated with the autoionization of the 4s-np singly excited states and the 4p4p-nln′l′ doubly excited states reproduces the results of recent measurements of total photoabsorption cross sections for the Rb+, Sr2+, and Y3+ ions. It is found that, as the nuclear charge in the isoelectronic sequence increases, the ratio between the direct and correlation parts of amplitudes of the 4s-(n/ɛ)p transition changes and, as the consequence, the minimum of the photoionization cross section of the 4s shell shifts from the continuous spectrum to the region of states of discrete spectrum. This accounts for the strong changes in the shape of the 4s-np resonances in the photoionization cross sections for the 4p shell of Rb+, Sr2+, and Y3+, as well as the distinction between the shapes of the 4s-6p1/2 mirror resonance in the partial 4p1/2 and 4p3/2 photoionization cross sections for the Y3+ ion which do not suppress each other in the total photoionization cross section, as is the case for similar resonances in Rb+ and Sr2+.