47 research outputs found
Unraveling the internal dynamics of the benzene dimer: a combined theoretical and microwave spectroscopy study
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Observing the First Stars and Black Holes
The high sensitivity of JWST will open a new window on the end of the
cosmological dark ages. Small stellar clusters, with a stellar mass of several
10^6 M_sun, and low-mass black holes (BHs), with a mass of several 10^5 M_sun
should be directly detectable out to redshift z=10, and individual supernovae
(SNe) and gamma ray burst (GRB) afterglows are bright enough to be visible
beyond this redshift. Dense primordial gas, in the process of collapsing from
large scales to form protogalaxies, may also be possible to image through
diffuse recombination line emission, possibly even before stars or BHs are
formed. In this article, I discuss the key physical processes that are expected
to have determined the sizes of the first star-clusters and black holes, and
the prospect of studying these objects by direct detections with JWST and with
other instruments. The direct light emitted by the very first stellar clusters
and intermediate-mass black holes at z>10 will likely fall below JWST's
detection threshold. However, JWST could reveal a decline at the faint-end of
the high-redshift luminosity function, and thereby shed light on radiative and
other feedback effects that operate at these early epochs. JWST will also have
the sensitivity to detect individual SNe from beyond z=10. In a dedicated
survey lasting for several weeks, thousands of SNe could be detected at z>6,
with a redshift distribution extending to the formation of the very first stars
at z>15. Using these SNe as tracers may be the only method to map out the
earliest stages of the cosmic star-formation history. Finally, we point out
that studying the earliest objects at high redshift will also offer a new
window on the primordial power spectrum, on 100 times smaller scales than
probed by current large-scale structure data.Comment: Invited contribution to "Astrophysics in the Next Decade: JWST and
Concurrent Facilities", Astrophysics & Space Science Library, Eds. H.
Thronson, A. Tielens, M. Stiavelli, Springer: Dordrecht (2008
An ab initio study of the rotation—vibration energy levels of GeH2 in the X̃1A1 state
Thirty-seven points on the potential-energy surface of the X̃1A1 ground electronic state for the GeH2 radical have been calculated using the (ab initio) MRD Cl technique. Twelve parameters in an analytic expression for the potential have been adjusted (by least-squares optimization) so that the surface fits these points. The rotation—vibration energy levels of GeH2 and GeD2 have been calculated using the non-rigid bender Hamiltonian, and we determine for GeH2 that ν1 = 1857 cm−1, ν2 = 923 cm−1 and ν3 = 1866 cm−1, in good agreement with the values obtained from a matrix-isolation spectrum. The equilibrium structure is found to be re = 1.591 A and αe = 91.4°
Vibrational magnetism and the strength of magnetic dipole transition within the electric dipole forbidden ν 2
Ion implantation processing for high performance concentrator solar cells and cell assemblies
Ab initio rotation-vibration energies and intensities for the H2F+ molecule
In a previous publication [I. D. Petsalakis, G. Theodorakopoulos, J. S. Wright, and I. P. Hamilton, J. Chem. Phys., 92, 2440-2449 (1990)] we reported the ab initio multireference configuration interaction calculation of the three-dimensional potential energy surface of the H2F+ molecule in the ground X ̃1A1 electronic state at 119 nuclear geometries spanning an energy range up to about 50 000 cm-1 above equilibrium. We fitted the 71 points within 33 000 cm-1 of equilibrium to an analytic expression and performed variational calculation of the vibrational energies in Jacobi coordinates using the Discrete Variable Representation and Distributed Gaussian Basis functions (DVR-DGB) technique. In the present paper we examine the effect on the vibrational energies of using a surface obtained by fitting through 52 points within 25 000 cm-1 of equilibrium. We use this surface in a variational calculation of the J = 0, 1, and 2 rotation-vibration energies using the Morse Oscillator Rigid Bender Internal Dynamics Hamiltonian [P. Jensen, J. Mol. Spectrosc., 128, 478-501 (1988); J. Chem. Soc. Faraday Trans. 2, 84, 1315-1340 (1988)]. The vibrational energies obtained are compared with those obtained by the DVR-DGB technique. We also calculate ab initio the dipole moment function and rotation-vibration intensities, and we simulate the ν2 band, which has not yet been observed