Observation of three weakly bound valence states of I2

Structured emission in the gas phase to two weakly bound valence states that correlate with the third dissociation limit, I*(2P1/2)+I*(2P1/2), designated as (bb), from two third tier ion-pair states of I2 correlating with I-(1S0)+I+(1D2), the 1g(1D2), and F'0u+(1D2) states, has been observed for the first time. The 1u(bb) state is shown to be bound by 377+/-2 cm(-1) and molecular constants have been determined. Vibrational structure in the 0g+(bb) state could not be resolved but the spectrum is consistent with the state being bound by 435 cm(-1). The relative integrated intensities of the emissions from both ion-pair states to various valence states have also been measured, and some aspects are rationalized in terms of the electronic configurations of the upper and lower states. Bound levels of a previously uncharacterized 1g(ab) valence state have also been observed in emission from the gamma1u(3P2) ion-pair state. The lower state is shown to be bound by 270+/-2 cm(-1) and molecular constants have been determined.     

Adaptive coded-aperture imaging with subpixel superresolution

We describe an adaptive coded-aperture imager operating in the midwave IR. This consists of a coded-aperture mask, a set of optics, and a 4k×4k focal plane array (FPA). This system can produce images with a resolution better than the detector pixel limit by combining multiple frames of data recorded with different coding. This superresolution capability has been demonstrated both in the laboratory and with targets placed outside, the highest resolution being one-half of the FPA pixel pitch.     

Characterization of the potential minimum of the F '0(u)(+)(1D2) ion-pair state of Cl2 using (1 + 2') optical-optical double resonance excitation and mass-resolved ion detection

Vibrational levels of the F(')0(u)(+)((1)D(2)), F0(u)(+)((3)P(0)), and D0(u)(+)((3)P(2)) ion-pair states of (35)Cl(2) and (35)Cl(37)Cl in the range 62,500-67,600 cm(-1) have been observed using (1 + 2(')) optical-optical double resonance excitation with mass-resolved ion detection. The strong F(')0(u)(+)((1)D(2))/F0(u)(+)((3)P(0)) coupling has been modelled by a coupled two-state calculation. An optimized fit of the experimental data used an F(')0(u)(+)((1)D(2)) state potential with a T(e) of 65,177 cm(-1) and an R(e) of ≈2.636 ? with a coupling constant of ≈430 cm(-1). The calculation assigns the first observed members of the F(')0(u)(+)((1)D(2)) state progression of (35)Cl(2) and (35)Cl(37)Cl at 64,998 and 65,094 cm(-1), respectively, as transitions to v = 0.     

Field induced ion-pair formation from ICl studied by optical triple resonance

Multiphoton pathways to the ion-pair states of ICl, at energies close to dissociation, are presented. These very high vibrational levels (v > or = 10(4)) are detected in the I+ and Cl- channels by pulsed field ionisation. Using a variable time delay before field ionisation, ion-pair states up to 50 cm-1 below the dissociation limit are shown to survive for at least 2 microseconds, indicating a stabilisation process analogous to that operating in high Rydberg electronic states. The atomic ion production signal is highly structured both above and below the free ion threshold, indicating the role of doorway states which are coupled to the dense ion-pair manifold near dissociation. This initial coupling appears to be very efficient and competes successfully with radiative decay and further up-pumping.     

Inelastic electron-acoustic-phonon interaction in quantum-well wires

Due to the lack of transverse momentum conservation for the electron-acoustic-phonon interaction in quantum wires this interaction becomes strongly inelastic within a wide range of electron energies. As a result the electron distribution function has to be found from an integro-differential equation. We derive the new nonequilibrium distribution functions for these conditions and present the electric field dependences for the kinetic coefficients. Our approach can be applied as well for two-dimensional electron systems or for electrons subjected to an external quantizing magnetic field. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 6, 441–446 (25 March 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

The NH2-inversion potential function in the Ã1b2 electronic state of aniline: Evidence for planarity

Values for the NH₂-inversion levels in the ùB₂ State of aniline-NH₂ and -ND₂ have been improved using new information regarding     

Tracing the pathways of neotropical migratory shorebirds using stable isotopes: a pilot study

We evaluated the potential use of stable isotopes to establish linkages between the wintering grounds and the breeding grounds of the Pectoral Sandpiper (Calidris melanotos), the White-rumped Sandpiper (Calidris fuscicollis), the Baird's Sandpiper (Calidris bairdii), and other Neotropical migratory shorebird species (e.g., Tringa spp.). These species molt their flight feathers on the wintering grounds and hence their flight feathers carry chemical signatures that are characteristic of their winter habitat. The objective of our pilot study was to assess the feasibility of identifying the winter origin of individual birds by: (1) collecting shorebird flight feathers from several widely separated Argentine sites and analyzing these for a suite of stable isotopes; and 2) analyzing the deuterium and 18O isotope data that were available from precipitation measurement stations in Argentina. Isotopic ratios (delta13C, delta15N and delta34S) of flight feathers were significantly different among three widely separated sites in Argentina during January 2001. In terms of relative importance in separating the sites, delta34S was most important, followed by delta15N, and then delta13C. In the complete discriminant analysis, the classification function correctly predicted group membership in 85% of the cases (jackknifed classification matrix). In a stepwise analysis delta13C was dropped from the solution, and site membership was correctly predicted in 92% of cases (jackknifed matrix). Analysis of precipitation data showed that both deltaD and delta18O were significantly related to both latitude and longitude on a countrywide scale (p < 0.001). Other variables, month, altitude, explained little additional variation in these isotope ratios. Several issues were identified that will likely constrain the degree of accuracy one can expect in predicting the geographic origin of birds from Argentina. There was unexplained variation in isotope ratios within and among the different wing feathers from individual birds. Such variation may indicate that birds are not faithful to a local site during their winter stay in Argentina. There was significant interannual variation in the deltaD and delta18O of precipitation. Hence, specific locations may not have a constant signature for some isotopes. Moreover, the fractionation that occurs in wetlands due to evaporation significantly skews local deltaD and delta18O values, which may undermine the strong large-scale gradients seen in the precipitation data. We are continuing the research with universities in Argentina with a focus on expanding the breadth of feather collection and attempting to resolve the identified issues.     

The 330-nm S1-S0 electronic spectrum of 1-pyrazoline: Probable hindered pseudorotation in S1 and confirmation of the ring-puckering potential function in S0 by single vibronic level fluorescence spectroscopy

The S₁-S₀ absorption spectrum of 1-pyrazoline is rotationally sharp but vibrationally extremely irregular, and other techniques are necessary to aid its assignment. The relaxed fluorescence spectrum shows a very long progression in the NN twisting vibration, suggesting that the ring is twisted in S₁ whereas, in S₀, this part of the ring is planar but the CH₂ group in position 4 is puckered. With a twisted ring in S₁ it seems likely that the NN twisting and CH₂(4) puckering modes in S₀ should be combined and newly described as radial and hindered pseudorotational modes in S₁. The vibronic transitions accompanying such an S₁-S₀ electronic transition are derived. Single vibronic level fluorescence spectra from many vibronic levels of S₁ show progressions in both the NN twisting and CH₂(4) puckering vibrations in S₀, but only with Δv even. This strongly supports the suggestion that these two modes are heavily mixed in S₁, and indicates that the fluorescing states are either above the barrier to pseudorotation or not far below it, so that there is appreciable tunnelling through the barrier. The progressions in the CH₂(4) puckering vibration allow us to assign uniquely the puckering quantum number, in S₀, of the band in which excitation took place. In addition, the spacings in these progressions further confirm the preferred potential function derived from the far-infrared spectrum and confirmed previously from the microwave spectrum.