9,600 research outputs found
Rotational branching ratios at low photoelectron energies in resonant enhanced multiphoton ionization of NO
We report calculated rotational branching ratios for very low energy (50 meV) photoelectrons resulting from (1+1â˛) resonant enhanced multiphoton ionization (REMPI) via the J_i =1/2, 3/2, 5/2, and 7/2 levels of the P_(11) branch of the Aâ^2ÎŁ^+ (3sĎ) state of NO. Even angular momentum transfer (ÎNâĄN_+âN_i) peaks are dominant in these rotational distributions, in agreement with the selection rule ÎN+l=odd. Angular momentum coupling in the photoelectron wave function arising from the molecular ion potential leads to smaller but appreciable ÎN=odd peaks. The calculated ÎN=0 to ÎN=+2 peak ratios show the same strong decrease when J_i increases from 1/2 to 3/2 as seen in the experimental zeroâkineticâenergy (ZEKE) photoelectron spectra [Sander et al., Phys. Rev. A 36, 4543 (1987)], but do not show the rapid dieâoff of the ÎNâ 0 peaks for higher J_i observed experimentally. The calculated trend in the ÎN=+2 vs ÎN=0 peaks could be understood on the basis of simple angular momentum transfer arguments. These same arguments indicate that this trend in the ÎN=0 and +2 peaks with increasing angular momentum is not generally expected in other branches. Spectra via the R_(21) (âJ) branch are presented to support this assertion. We also present photoelectron angular distributions which show a strong dependence on ÎN reflecting the changing composition of the photoelectron wave function
On the Consistent Effect Histories Approach to Quantum Mechanics
A formulation of the consistent histories approach to quantum mechanics in
terms of generalized observables (POV measures) and effect operators is
provided. The usual notion of `history' is generalized to the notion of `effect
history'. The space of effect histories carries the structure of a D-poset.
Recent results of J.D. Maitland Wright imply that every decoherence functional
defined for ordinary histories can be uniquely extended to a bi-additive
decoherence functional on the space of effect histories. Omnes' logical
interpretation is generalized to the present context. The result of this work
considerably generalizes and simplifies the earlier formulation of the
consistent effect histories approach to quantum mechanics communicated in a
previous work of this author.Comment: LaTeX 2.09 version replaced by LaTeX2e version, minor change
Photoionization cross sections of rovibrational levels of the B^1ÎŁ^+_u state of H_2
We report theoretical cross sections for direct photoionization of specific rovibrational levels of the Bâ^1ÎŁ^+_u electronic state of H_2. The calculated cross sections differ considerably from values recently determined by resonant enhanced multiphoton ionization (REMPI) studies. In an attempt to understand the disagreement, we analyze in detail the REMPI dynamics and find that the multiphoton ionization probability is extremely sensitive to the spatial and temporal profiles of the laser pulses. Accurate characterization of laser profiles and their jitter is therefore necessary for a comparison between theory and experiment
Fractional Energy Loss and Centrality Scaling
The phenomenon of centrality scaling in the high-\pt spectra of
produced in Au-Au collisions at GeV is examined in the framework
of relating fractional energy loss to fractional centrality increase. A new
scaling behavior is found where the scaling variable is given a power-law
dependence on . The exponent specifies the fractional
proportionality relationship between energy loss and centrality, and is a
phenomenologically determined number that characterizes the nuclear suppression
effect. The implication on the parton energy loss in the context of
recombination is discussed.Comment: 4 pages in RevTe
Why don't clumps of cirrus dust gravitationally collapse?
We consider the Herschel-Planck infrared observations of presumed
condensations of interstellar material at a measured temperature of
approximately 14 K (Juvela et al., 2012), the triple point temperature of
hydrogen. The standard picture is challenged that the material is cirrus-like
clouds of ceramic dust responsible for Halo extinction of cosmological sources
(Finkbeiner, Davis, and Schlegel 1999). Why would such dust clouds not collapse
gravitationally to a point on a gravitational free-fall time scale of
years? Why do the particles not collide and stick together, as is fundamental
to the theory of planet formation (Blum 2004; Blum and Wurm, 2008) in pre-solar
accretion discs? Evidence from 3.3 m and UIB emissions as well as ERE
(extended red emission) data point to the dominance of PAH-type macromolecules
for cirrus dust, but such fractal dust will not spin in the manner of rigid
grains (Draine & Lazarian, 1998). IRAS dust clouds examined by Herschel-Planck
are easily understood as dark matter Proto-Globular-star-Cluster (PGC) clumps
of primordial gas planets, as predicted by Gibson (1996) and observed by Schild
(1996).Comment: 8 pages, 2 figures, Conference FQMT'1
Hourly Variability in Q0957+561
We have continued our effort to re-reduce archival Q0957+561 brightness
monitoring data and present results for 1629 R-band images using the methods
for galaxy subtraction and seeing correction reported previously. The new
dataset comes from 4 observing runs, several nights apiece, with sampling of
typically 5 minutes, which allows the first measurement of the structure
function for variations in the R-band from timescales of hours to years.
Comparison of our reductions to previous reductions of the same data, and to
r-band photometry produced at Apache Point Observatory shows good overall
agreement. Two of the data runs, separated by 417 days, permit a sharpened
value for the time delay of 417.4 days, valid only if the time delay is close
to the now-fashionable 417-day value; our data do not constrain a delay if it
is more than three days from this 417-day estimate. Our present results show no
unambiguous signature of the daily microlensing, though a suggestive feature is
found in the data. Both time delay measurement and microlensing searches suffer
from from the lack of sampling at half-day offsets, inevitable at a single
observatory, hence the need for round-the-clock monitoring with participation
by multiple observatories.Comment: AASTeX 4.0 preprint style, 21 pages, 8 EPS figure
Evolution of primordial planets in relation to the cosmological origin of life
We explore the conditions prevailing in primordial planets in the framework
of the HGD cosmologies as discussed by Gibson and Schild. The initial stages of
condensation of planet-mass H-4He gas clouds in trillion-planet clumps is set
at 300,000 yr (0.3My) following the onset of plasma instabilities when ambient
temperatures were >1000K. Eventual collapse of the planet-cloud into a solid
structure takes place against the background of an expanding universe with
declining ambient temperatures. Stars form from planet mergers within the
clumps and die by supernovae on overeating of planets. For planets produced by
stars, isothermal free fall collapse occurs initially via quasi equilibrium
polytropes until opacity sets in due to molecule and dust formation. The
contracting cooling cloud is a venue for molecule formation and the sequential
condensation of solid particles, starting from mineral grains at high
temperatures to ice particles at lower temperatures, water-ice becomes
thermodynamically stable between 7 and 15 My after the initial onset of
collapse, and contraction to form a solid icy core begins shortly thereafter.
Primordial-clump-planets are separated by ~ 1000 AU, reflecting the high
density of the universe at 30,000 yr. Exchanges of materials, organic molecules
and evolving templates readily occur, providing optimal conditions for an
initial origin of life in hot primordial gas planet water cores when adequately
fertilized by stardust. The condensation of solid molecular hydrogen as an
extended outer crust takes place much later in the collapse history of the
protoplanet. When the object has shrunk to several times the radius of Jupiter,
the hydrogen partial pressure exceeds the saturation vapour pressure of solid
hydrogen at the ambient temperature and condensation occurs.Comment: 14 pages 7 figures SPIE Conference 7819 Instruments, Methods, and
Missions for Astrobiology XIII Proceedings, Aug 3-5, 2010, San Diego, Ed.
Richard B. Hoove
(2+1) resonant enhanced multiphoton ionization of H_2 via the E, F^(1)ÎŁ^+_g state
In this paper, we report the results of ab initio calculations of photoelectron angular distributions and vibrational branching ratios for the (2+1) REMPI of H_2 via the E, F^(1)ÎŁ^+_g state, and compare these with the experimental data of Anderson et al. [Chem. Phys. Lett. 105, 22 (1984)]. These results show that the observed nonâFranckâCondon behavior is predominantly due to the R dependence of the transition matrix elements, and to a lesser degree to the energy dependence. This work presents the first molecular REMPI study employing a correlated wave function to describe the Rydbergâvalence mixing in the resonant intermediate state
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