S. Lahmar

Spectroscopy and metastability of BeO

The potential energy curve of the ground electronic state of BeO and those of the lowest electronic states of the BeO+ cation are computed using the CASSCF/MRCI methods and a large basis set. For the cation, the spin–orbit coupling and the transition momentum integrals are also evaluated. These data are used later to deduce an accurate set of spectroscopic constants and to investigate the spin–orbit-induced predissociation of the lowest electronic excited states of BeO+. Our calculations show that the high-rovibrational levels of the BeO+ (12Σ+) electronic state exhibit rapid predissociation processes forming Be+(2S) + O(3P). Our curves are also used for predicting the single ionization spectrum of BeO.

Stable and metastable states of SN

Highly correlated ab initio methods were used in order to generate the potential energy functions (PEFs) of the bound electronic states of the SN− anion and the long-range parts of the PEFs of its excited states and their mutual spin–orbit couplings. The SN (X2Π and a4Π) potential energy curves are also computed. In addition to the two bound electronic states of SN− (i.e. X3Σ− and 1Δ) already known, our calculations show that the 3Δ state is lying energetically below its quartet parent neutral state (a4Π). The depletion of the J = 3 component of SN−(3Δ) will mainly occur via weak interactions with the electron continuum wave. At large internuclear distances, SN−(5Π) state is predicted to possess a shallow polarization minimum supporting long-lived SN− ions. Finally, the reaction between S−(2Pu) and N(4Su) involves the electronic states of SN− and their mutual couplings, in competition with the autodetachment processes.

THEORETICAL SPECTROSCOPIC DATA FOR THE X2B1 AND A2A1 STATES OF H2S

Abstract Coupled electron pair (CEPA) electronic wave functions have been used to calculate the three-dimensional potential energy functions of the two lowest doublet states X2B1 and A2A1 of H2S+. The near-equilibrium potential for the X2B1 state has been used in variational calculations of the ro-vibrational energy levels up to 10 000 cm−1. Rotationally resolved absorption spectra of the three fundamental transitions have been calculated ab initio using the three-dimensional electric dipole moment functions and the ro-vibrational eigenfunctions. The absolute line strengths are given for the most intense transitions.

Spectroscopy and metastability of the HSS− anion§

Accurate ab initio calculations on the potential energy surfaces (PESs) of the lowest electronic states of the neutral HSS and those of the electronic states of the HSS− negative ion correlating to the bound asymptotes of this molecular system, reveal that the ground state of HSS− (i.e. 1A′) and the long range parts of the anionic PESs are stable against the autodetachment processes. In light of these calculations, the [HS + S]− and [S2 + H]− reactive systems are examinated and found forming the HSS− ( 1A′) ions either directly or after spin–orbit and/or vibronic and/or Renner–Teller couplings, in competition with fast electron loss processes. The three-dimensional PES of the unique bound electronic state of HSS− (i.e. 1A′) is generated using the coupled cluster approach and a large basis set. A set of spectroscopic parameters for HSS−/DSS− ( 1A′) and their vibrational spectra up to 3700 cm−1 are deduced from the 3D PES. §Dedicated to Professor Pavel Rosmus on his retirement.

Active learning in physics a way for rational thinking, a way for development

Science Development leads to new concepts, new tools and new techniques. It leads to a society development with new Truth. This Truth is shared by the Society which development is built on Knowledge, on rationality thinking and scientific behavior. This takes its origin in the experimental approach introduced by Ibn Al Haythem in optics at the Xth century. By the end of the last millennium, this approach-known as Active Learning in Physics- has been adopted in most developed countries in physics education programs. Active Learning in Optics and Photonics- ALOP- is extended actually to some developing countries through a UNESCO program. A French edition of ALOP takes place through many workshops over Morocco and Tunisia. It aims to build Truth on evidence and not on intuition or personal authority.

Optics simulations with Python: diffraction

Python is an easy open source software that can be used to simulate various optical phenomena. We have developed a suite of programs, covering both geometrical and physical optics. These simulations follow the experimental modules used in the ALOP (Active Learning in Optics and Photonics) UNESCO program in the sense that they complement it and help with student prediction of results. We present these programs and the student reactions to these simulations.

Vibrational motion in the state of LiSH and LiSD

We have generated an ab initio three-dimensional potential energy surface (PES) for the state of LiSH. The spectroscopic data calculated from a full quartic force field are in very good agreement with the values obtained from microwave spectroscopic experiments. The PES has been used to solve variationally the nuclear motion problem and the vibrational energy levels are given up to about 3500 cm−1 for LiSH and 2400 cm−1 for LiSD. For LiSH, the anharmonic fundamental modes lie at 2571 (SH stretch), 578 (LiS stretch) and 372 (LiSH bending), and for LiSD the corresponding values are: 1866, 582 and 276 (all values are in cm−1), respectively. Anharmonic resonances between the bending and the LiS stretching modes are identified in both species. The calculated electric dipole moment μ e = 7.03 debye mirrors the strong charge separation in the lithium hydrosulphide. The electronically excited states up to vertical transition energies of 36 000 cm−1 predissociate along the Li … SH path.

Workshop on Active Learning: Two Examples

Optics is an enabling science that has far ranging importance in many diverse fields. However, many students do not find it to be of great interest. A solution to this problem is to train teachers in active learning methodologies so that the subject matter can be presented to generate student interest. We describe a workshop to present an example of an active learning process in Optics developed for training of teachers in developing countries (a UNESCO project) and will focus on 2 two different activities: 1. Interference & diffraction is considered by students as being very hard to understand and is taught in most developing countries as purely theoretical with almost no experiments. Simple experiments to enhance the conceptual understanding of these wave phenomena will be presented and 2. Image formation by the eye. Here we will discuss myopia, hyperopia and astigmatism as well as accommodation. In this module we will discuss image. The objective of the workshop will be to provide an experience of the use of the active learning method in optics including the use of experiments, mind’s on & hands-on exercises, group & class discussions

Theoretical study of the MgSH radical

Abstract Ab initio RCCSD(T) and MRCI calculations have been carried out for the ground and excited electronic states of MgSH. For the X2A′ state a quartic force field has been generated using the RCCSD(T) approach and spectroscopic constants for MgSH and MgSD have been obtained from standard second order perturbation theory. The bent equilibrium geometry is found to be in a reasonably good agreement with previous empirical values. The anharmonic fundamental wavenumbers (in cm−1) are calculated to be 408 (MgS stretch), 470 (bending) and 2572 (SH stretch) for MgSH, whereas the lowest frequency in MgSD at 330 corresponds to the bending, the MgS stretch is calculated to lie at 421 and the SD stretch at 1867 (all values are in cm−1). For the low-lying doublet and quartet excited states the Mg⋯SH and MgS⋯H colinear paths to dissociation asymptotes are calculated and several regions of conical intersections are located. It is found that the first two 2Π lead to bent/bent Renner–Teller pairs, but their 2A′ components form a conical intersection for an apex angle around 140°. Hence all four resulting electronic components are rovibronically coupled. As in other alkaline-earth monohydrosulfide the future experimental electronic spectra between the ground and A, B and C doublet states, calculated to lie at 23000–26000 cm−1, could provide additional information about this radical.

Theoretical study of electron exchange in Mg2+–B collisions

The electron capture of Mg 2+ ions in collisions with boron atoms has been investigated using ab initio quantum chemical approaches. The potential energies of the electronic states implicated in the process together with the non adiabatic coupling matrix elements have been calculated by multi-reference configuration interaction methods. Total and partial cross sections for the charge transfer reaction are determined in the (1–600) keV impact energy range by means of semiclassical approaches. A detailed analysis of the electron capture mechanism taking into account radial and rotational interactions has been performed and compared to previous studies on collision systems involving the Mg 2+ projectile ion.