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Investigates the misconceptions in physics among South African students. The physics test which was administered to selected high school and college students is included. (HM)

We have investigated electron transfer to O4+ in reactions with O2, NO, and Cs. We observe formation of O4 molecules that decay by predissociation and by direct dissociation. The kinetic energy release in dissociation as well as the nature of the dissociation products are determined. Evidence for three short-lived electronic states of tetraoxygen at energies near 2 eV above O2+O2 is obtained in electron transfer from O2 and NO. In the experiment with cesium we find evidence for longer-lived electronic states (10-13≤τ≤10-7 s) at 9.4 and 10.5 eV. The energy release and symmetry of the dissociation pattern suggests that the high lying states are symmetric molecular configurations at extended bond lengths (∼2.4 Å). [ABSTRACT FROM AUTHOR]

Electronic absorptions leading to predissociation of the HF+ ion are observed by coaxial laser-ion beam photofragment spectroscopy. The absorptions occur in the A 2Σ+←X 2Π system and terminate in the N=4, v=3 level of the A state which predissociates into H++F. The (3,4) band of this system is observed for the first time and the observations extend earlier emission measurements in the (3,0) and (3,2) bands to higher rotational levels. In addition, the nuclear hyperfine structure of the ion is observed. Extended molecular constants are derived for the X and A states and the first values are given for the hyperfine structure constants of the A state. [ABSTRACT FROM AUTHOR]

A two-step photoionization scheme is used to determine vibrational frequencies of the n=3 Rydberg states of triatomic hydrogen. Symmetric-stretch frequencies in orthotrihydrogen of 3212.1 and 3168 cm-1 are measured for the N=1 levels of the states 3s 2A’1 and 3d 2E‘, respectively. Transitions to bending-mode excited levels in the 3d states and overtone levels of the 3p 2 E’ state are observed also. [ABSTRACT FROM AUTHOR]

Photodissociation of O2 is observed by direct detection of coincident neutral photofragments following laser excitation of a fast molecular beam. The O2 beam was prepared by charge-transfer neutralization of keV energy O+2 and irradiated by a linearly polarized, line selected Kr+ ion laser. Kinetic-energy resolved photofragments were observed at eight laser lines between 752.5 and 476.2 nm. Correlation of the observed fragment kinetic energies with laser wavelength shows that the observed photodissociations arise from O2 B 3σ-u(v’=1–18)←X 3σ-g (v‘=22–37) Schumann–Runge transitions. [ABSTRACT FROM AUTHOR]

Predissociation in several singlet valence and Rydberg states of molecular nitrogen has been investigated using photofragment spectroscopy. We report here measurements of the yields of the atomic fragment products N(4S0), N(2D0), and N(2P0) from predissociation of specific rotational levels in the b’ 1Σu+ (v=9–13), c’ 1Σu+ (v=3,4), c 1Πu (v=3,4), and o 1Πu (v=3) states of N2. These states are prepared by laser excitation from the metastable a‘ 1Σg+ (v=0) level in a fast (3 keV) molecular beam. Correlated atomic fragments from single molecular dissociation events are monitored using a position- and time-sensitive detector to obtain a complete and sensitive scheme for all possible N2 dissociation products. Dissociation of the N2 states is found to occur to N(2D0)+N(4S0), and N(2P0)+N(4S0) products; production of N(4S0)+N(4S0) is found not to occur from any of the states investigated here. Branching of the dissociation products between the two active limits is found to be strongly correlated with the energy of the predissociating level: levels lying <112 200 cm-1 above N2 X 1Σg+ (v=0) predissociate primarily to the N(2D0)+N(4S0) limit, while states above this energy primarily predissociate to N(2P0)+N(4S0). This behavior is discussed in terms of the potential energy structure of the triplet states of nitrogen that lead to predissociation. [ABSTRACT FROM AUTHOR]

We measured the survival probability of the metastable (N=0, K=0) level of the 2p2A‘2 of H3 as a function of time elapsed from formation of the molecule by probing its population with photoionization. We find lifetimes τ=640+300-100 ns for the ground vibrational state and τ=740+300-100 ns for the symmetric stretch-excited level. Equally short lifetimes are obtained from an analysis of the photoinduced bleaching of the spontaneous dissociation signal of metastable H3. These lifetimes are about 2 orders of magnitude shorter than those expected on the basis of the allowed radiative transition 2p2A‘2→2s2A’2. We attribute the faster decay channel to weakly allowed radiative transitions between the metastable state and the degenerate mode-excited repulsive ground state of H3, as well as to predissociation of the metastable levels by the repulsive ground state of H3 induced by spin–orbit coupling. [ABSTRACT FROM AUTHOR]

A double-resonance technique is employed to measure the positions of energy levels of the second 3Πg state of H2. Vibrational levels of this state with v>3 lie above the ionization threshold of H+2, and are observed both to autoionize and dissociate. This state, 23Πg, arises from the homogeneous interaction between the singly excited 1sσg3dπg and 1sσg4dπg diabatic Rydberg states with the core-excited 2pσu2pπu state. The energy-level spacings are in good agreement with a simple model calculation for the interacting potentials. We also include a listing of autoionizing levels lying in the same energy range. [ABSTRACT FROM AUTHOR]