A.H. de Lange

Predissociation in b1Pu, v (v=1,4,5,6) levels of N2

In a high-resolution laser spectroscopic study, using a tunable Fourier-transform limited light source in the extreme ultraviolet, the b 1Πu excited valence state of molecular nitrogen is reinvestigated for vibrational levels v=1, 4, 5, and 6. From line broadening of individual rotational levels excited state lifetimes were determined: τ(v=1)=1.1±0.3 ns, τ(v=4)=18±1 ps, τ(v=5)=205±25 ps, and τ(v=6)=350±75 ps. Additionally, the lifetime of the o3 1Πu, v=0 Rydberg state was determined: τ=240±50 ps. For the b 1Πu, v=1 state improved rotational constants were determined.

Observation of the I ' (1)Pi(g) outer well state in H-2 and D-2

We observed bound levels of the I′ state in H2 and D2, confined in the outer well of the lowest 1Πg adiabatic potential close to its (1s+2p) dissociation limit, with an equilibrium internuclear distance of ≈8 a.u. Rovibronic levels (v=0–2, J=1–5 for H2 and v=0–5, J=1–6 for D2) are populated with pulsed lasers in resonance enhanced XUV+IR (extreme ultraviolet+infrared) excitation, and probed by a third laser pulse. Level energies are measured with an accuracy of ≈0.03 cm−1, and are in reasonable agreement with predictions from ab initio calculations in adiabatic approximation; the smallness of Λ-doublet splitting indicating that nonadiabatic interactions with 1Σg+ states are generally weak. Additional resonances are observed close to the n=2 dissociation limit, some of which can be assigned as high vibrational levels of the EF 1Σg+ state.

Phenomena of g-u symmetry-breakdown in HD

Phenomena associated with the breakdown of inversion symmetry in the HD molecule are reviewed and discussed. A distinction is made between three kinds of physical effects observed in HD spectra. The existence of a small electric dipole moment in the ground state gives rise to vibrational and pure rotational transitions following selection rules of electric dipole transitions. Coupling between electronic states of g and u symmetry occurs, which is associated with the appearance of forbidden lines in the electronic spectrum. This effect occurs predominantly at near coincidences between levels of opposite inversion symmetry and a recently observed example of strongly interacting states (H¯ 1 + g and B¯ 1 + u ) is highlighted. Electronic coupling between states of g and u symmetry always takes place near dissociation threshold; as a result of the mass difference and the electronic isotope shift the behaviour at long range cannot be described in an adiabatic picture. A procedure is developed to construct long-range potentials near the n = 2 dissociation limit in which the breakdown of g-u symmetry is incorporated.

Search for outer-well states above the ionization potential in H2

Recent ab initio calculations by Detmer et al. [J. Chem. Phys. 109 (1998) 9694] and by Staszewska and Wolniewicz [ J. Mol. Spectr. 212 (2002) 208] have produced potential energy curves in the energy region between the n=3 and n=4 dissociation limits in hydrogen, that in principle support bound states of an exotic nature. They are confined to large internuclear separation (R>10 a.u.) by a potential barrier giving the H2 molecule an unusually large size. In an experimental study involving a four-laser excitation scheme such states were searched for, but the dominant feature observed in this energy region is that of a direct continuum excitation when probing states of ungerade symmetry. An analysis in terms of a Landau–Zener tunneling model predicts that all vibrational levels in the 61Σ+u state, perhaps with exclusion of the v=0 level, are subject to rapid predissociation.

Bound energy levels at the n=2 dissociation threshold in HD

Level energies of g symmetry states lying just below the n ¼ 2 dissociation threshold have been determined in a XUV + IR multi-step laser excitation experiment in HD, with an absolute accuracy of the excitation energy of 0.015 cm � 1 . Intermediate B 1 R þ energy levels have been calibrated by measuring transition frequencies in the B 1 R þ –X 1 R þ ð16; 0Þ Lyman band with an accuracy of 0.007 cm � 1 . It is shown that v ¼ 3 is the highest bound vibrational level in the shallow I 01 Pg outer well potential in HD, and that only two rotational levels exist.

Leren op de werkplek en duurzame inzetbaarheid

SamenvattingLeren op de werkplek kan de duurzame inzetbaarheid van werknemers bevorderen mits er sprake is van maatwerk. Een recent onderzoek door Van der Heijden en collega’s (2015) focuste op de kansen die leren op de werkplek biedt om duurzame inzetbaarheid te realiseren. Duidelijk is: baan én baas moeten de werknemer uitdagen!