J. Schamps

Laser spectroscopy of CaBr: A2Π-X2Σ+ and B2Σ+-X2Σ+ systems

Abstract Laser excitation spectra have been recorded for Ca 79 Br and Ca 81 Br in the spectral region 600–630 nm. The use of a 1-m monochromator as a narrow band pass filter (1–2 cm −1 ) has allowed rotational analysis of the 0-0, 1-1, and 2-2 bands of the B 2 Σ + - X 2 Σ + transition and the 0-0 and 1-1 bands of the A 2 Π - X 2 Σ + transition. A few additional lines of the 0-1, 1-2, 1-0, and 2-1 bands of the B - X system were used to obtain band origins for vibrational analysis. The main constants for Ca 79 Br are (in cm −1 ): X 2 Σ + A 2 Π B 2 Σ + T e 0 15 958.41 (10) 16 383.137 (6) ω e 285.732 (9) 288.56 (20) 285.747 (9) ω e χ e 0.840 (4) — 0.954 (4) B e 0.094466141 (30) 0.0957343 (20) 0.0965151 (20) α e 0.000403551 (40) 0.0004327 (20) 0.0004483 (15) γ e (spin-rot.) 0.00301484 (50) — 0.068767 (79) P e — −0.066834 (64) — A e — 59.175 (1) — (All uncertainties are 1σ.) The usual isotope relations between the constants for Ca 79 Br and Ca 81 Br are satisfied to within 3σ. The A and B states form a unique perturber pair with l eff = 1.24.

Ab initio study of the three lowest‐lying (X 1Σ+, 3Σ+, and 1Σ+) electronic states of AgF

Ab‐initio pseudopotential two‐configuration self‐consistent field followed by extensive variational and perturbational second order Mo/ller–Plesset multireference configuration interaction calculations using localized molecular orbitals were performed to characterize the structure and adiabatic potential energy curves of the three lowest (X 1Σ+, 3Σ+, and 1Σ+) purely electronic states of the AgF molecule. Spin‐orbit interactions were introduced semiempirically in a second step. The very strong coupling of the neutral Ag(4d105s1)F(2s22p5) and ionic Ag+(4d95s1)F−(2s22p6) configurations at rather short internuclear distance for both excited 3,1Σ+ states is responsible for the appearance of very shallow minima, thus leading to a limited number of stable vibrational levels for these excited states as suggested previously for the AO+ state. In contrast with the CuF molecule, where only the ionic configuration Cu+(3,1D)F−(1S) is present in the 3,1Σ+ states, this coupling of ionic and neutral structures in AgF is ...

The electronic structure of LaO: Ligand field versus ab initio calculations

The potentially pathological example of LaO has been chosen to test the application of ligand field theory (LFT) to metal monoxides. The test consists of a comparison of closed‐shell ligand LFT (CSLLFT) results (in which a 2+/2− ionic M2+O2− model is a priori postulated with a point‐charge ligand) against ab initio multiconfiguration self‐consistent‐field–multireference configuration interaction (MCSCF‐MRCI) results (in which no ionicity is assumed a priori and an internal structure is allowed for the ligand). Special care has been devoted to the determination of a La3+ pseudopotential and its associated atomic basis set in order to keep the ab initio model close to the LFT one, yet at the same time capable of clearly exhibiting the consequences and the importance of the restrictions imposed in the CSLLFT model. The ab initio calculations reveal that the effective (Mulliken) ionicity in LaO is not La2+O2− but quite close to La+O−. Despite this, the (2+/2−) ionic CSLLFT model leads to the correct orbital o...

Radiative lifetimes of the excited electronic states of CuCl

Spontaneous radiative lifetimes of the observed electronic states of CuCl have been calculated using a model including spin–orbit interaction mixings within the Cu+(3d94s)Cl−(3s23p6) structure. The required wave functions have been determined semiempirically and locations of the as‐yet unobserved components have been estimated. For the A 3Σ1+, C 3Π0e, D 1Π1, E 1Σ0+, and F 3Δ1 components, the lifetimes calculated in the simple single‐configuration pure‐precession approximation with a slight modification in the Ω=0e block are in good agreement with earlier experimental measurements. On the contrary, for the B 3Π1 component, there is a marked discrepancy that cannot be reduced except by assigning very unlikely values to the off‐diagonal spin–orbit parameters.

The electronic spectrum of PrO. Energy linkages, rotational analysis, and hyperfine structure for systems XVII and XXI

Abstract Doppler-limited laser excitation spectra for four bands of PrO have been recorded: System XvII 0-0, System XXI 0-0 and 0–1, and the 0-0 intercombination between the upper and lower states, respectively, of Systems XVII and XXI. First lines in R and P branches prove that Systems XVII and XXI are, respectively, Ω ′ = 4.5 − Ω ″ = 3.5 and Ω ′ = Ω ″ = 4.5 . Hyperfine components are well resolved for all four excitation bands. Rotational and hyperfine constants are determined by least-squares fits of data from all four bands together. In addition, fluorescence spectra, recorded from various J′, v′ = 0 levels of the upper states of Systems XVII and XXI, reveal five new low-lying states. Principal constants (in cm−1) for nine Ω-states follow (1σ uncertainty in parentheses): State T v B v d (hfs) Ω′ = 4.5 (System XXI) 18 882.388 (2) 0.353001 (18) 0.12403 (71) Ω′ = 4.5 (System XVII) 16 594.075 (1) 0.353736 (20) 0.12977 (67) Ω ″ = 3.5 3 887.15 (16) 0.35751 (28) — Ω ″ = 3.5 2 931.66 (15) 0.35712 (21) — Ω ″ = 4.5 2 155.16 (30) 0.36264 (67) — Ω ″ = 5.5 2 099.16 (31) 0.35079 (71) — Ω ″ = 3.5 2 064.34 (13) 0.35654 (20) — Ω″ = 4.5 (System XXI) 217.383 (1) 0.362134 (20) 0.27744 (66) Ω″ = 3.5 (System XVII) 0.0 0.360948 (16) −0.00809 (85)

Ab initio embedded cluster study of the excitation spectrum and Stokes shifts of Bi3+-doped Y2O3.

The ab initio embedded cluster method coupled with correlated spin-orbit calculations has been used to interpret the excitation spectrum of a Bi(3+)-doped yttria crystal. Our results indicate that the Bi(3+) impurity can absorb light over a wider energy range in the C(2) site than in the S(6) site. Even if the computed absorption energies seem to be about 0.4 eV too high with respect to the experimental peaks for both sites, it is noteworthy that the embedded cluster model renders 93% of the large crystal redshift, about 6 eV. The determination of the geometry relaxation of the first shell of oxygen neighbors upon electronic excitation shows that the Stokes shift is smaller in the S(6) site than in the C(2) site. Combining all these results confirms the assignment of the violet emission to the S(6) site and that of the green emission to the C(2) site, as proposed by Boulon [J. Phys. (Paris) 32, 333 (1971)]. In addition, the nature of the metastable states which lie below the emitting ones and are responsible for the temperature dependence of the fluorescence lifetimes is discussed.

Ab initio computation of radiative lifetimes of the valence electronic states of CuF

Abstract Radiative lifetimes of all the electronic states of CuF belonging to the Cu + (3d 9 4s)F − (2p 6 ) structure have been calculated using spin-orbit-perturbed ab initio SCF Cl wavefunctions. Calculated energies, in very good agreement with experiment, and dipole moments for the ground and excited states are given. Although configuration interaction is only significant in the X and B 1 Σ + states, it is shown to play the essential part in the calculated lifetime values. Thus the simple model in which the observed transitions of CuF are thought of as being atomically forbidden 3d–4s transitions made allowed by molecular polarization of the orbitals completely fails. In spite of the subtlety of the processes involved good agreement is obtained for the three states for which experimental data are available (B 1 Σ, C 1 Π, A 3 Π 0 c ,1 ). Lifetime values are predicted for the other states. especially for the observed ones: τ(D 3 Δ 1 ) = 54 us. Absorption oscillator strengths are given for all the transitions starting. from the X 1 Σ + ground state.

Perturbations in the A1Π-X1Σ+ system of the BeS molecule. The a3Πi state

Abstract The states responsible for all perturbations observed by Cheetham et al. [Trans. Faraday Soc. 61, 1308–1316 (1965)] in the BeS A1Π-X1Σ+ system were electronically (a3Π2, a3Π1, and X1Σ+) and vibrationally assigned. Cheetham et al. had incorrectly suggested that perturbations presently assigned as A1Π(vA) ∼ a3Π2(va = vA + 2) were A 1 Π ∼ 1 Δ . Molecular constants for the newly identified a3Πi state, which is the lowest energy excited state of BeS, as well as electronic parameters for A ∼ X, A ∼ a, and a ∼ X interactions were determined. Principal constants (in cm−1) for A1Π and a3Π are a 3 Π A 1 Π T e 7 100 (75) 7 961.64 (26) ω e 737 (5) 762.13 (7) ω e χ e 4.1 (2) 4.09 (4) r e ( A ) 1.9190 (10) 1.9087 (2) (1σ uncertainties in parentheses). A coherent picture of the perturbations in A1Π could be drawn only by combining fragmentary spectroscopic data from Cheetham et al. with new ab initio calculations of spin-orbit and rotation-electronic perturbation parameters, spin-orbit splittings, and energy separations of isoconfigurational a3Π and A1Π states.

MCSCF+MRCI calculation of diagonal and transition dipole moments in CuCl

Abstract The zeroth- and first-order (Moller-Plesset) MRCI wavefunctions for the nine lowest-lying electronic states of CuCl are used to calculate diagonal and transition dipole moments. For the diagonal dipole moments the MCSCF molecular orbitals were used thus leading to accurate results. In the case of transition moments, the MCSCF MOs of one state or those of the other were used to avoid problems involved with nonorthogonal basis sets. The calculated electronic transition dipole moments between ionic excited states are found to be so small that these infrared radiative channels are insignificant compared to the visible ones, at least for the observed states. This confirm earlier assignments based on measured lifetimes, except for the A state that is now thought to be 3 Σ + rather than 3 π 2 .

A calculation of radiative lifetimes of electronically excited rovibronic levels of CuF

Abstract Radiative lifetimes for rovibronic levels of the excited valence states of CuF are calculated using a model including both spin-orbit and Coriolis interactions. According to a discussion concerning their decay mechanisms, the spin-orbit components are classified into three classes with lifetimes differing by several orders of magnitude. Electronic transition intensity patterns are calculated and compared with spectroscopic observations.