Engineering topics

Prasad, Sheo S.

Publications and source records attributed to Prasad, Sheo S..

5 records

NASA NTRS1994

Atmospheric chemistry of the reaction ClO + O2 reversible reaction ClO (center dot) O2: Where it stands, what needs to be done, and why?

Possible existence and chemistry of ClO (center dot) O2 was originally proposed to explain the Norrish-Neville effect that O2 suppresses chlorine photosensitized loss of ozone. It was also thought that ClO (center dot) O2 might have some atmospheric chemistry significance. Recently, doubts have been cast on this proposal, because certain laboratory data seem to imply that the equilibrium constant of the title reaction is so small that ClO (center dot) O2 may be too unstable to matter. However, those data create only a superficial illusion to that effect, because on a closer analysis they do not disprove a moderately stable and chemically significant ClO (center dot) O2. Furthermore, our state-of-the-science accurate computational chemistry calculations also suggest that ClO (center dot) O2 may be a weakly bound ClOOO radical with a reactive (2)A ground electronic state. There is therefore a need to design and perform definitive experimental tests of the existence and chemistry of the ClO (center dot) O2 species, which we discuss and which have the potential to mediate the chlorine-catalyzed stratospheric ozone depletion.

Prasad, Sheo S.↗

NASA NTRS1991

Dynamical evolution and molecular abundances of interstellar clouds

Dynamical models are presented that start with interstellar gas in an initial diffuse state and consider their gravitational collapse and the formation of dense cores. Frozen-in tangled magnetic fields are included to mimic forces that might oppose gravitational contraction and whose effectiveness may increase with increasing core densities. Results suggest the possibility that dense cloud cores may be dynamically evolving ephemeral objects, such that their lifespan at a given core density decreases as that density increases.

Prasad, Sheo S.↗

NASA NTRS1991

Dynamical conditions of dense clumps in dark clouds - A strategy for elucidation

Chemical considerations and simplified dynamical modeling suggest that dark cloud cores may be incessantly evolving such that the time spent at high core densities decreases as the density increases. After reaching a high density, gravitationally contracting dark cloud cores may either form stars or expand to states of lower densities. Cloud mass and initial density are amongst the factors that may control the evolutionary fate of the core. This view is diametrically opposite of the common belief that dense cores may be in near mechanical equilibrium. Mutually consistent end-to-end modeling of the spectral line profiles and intensities is needed to discern the reality.

Prasad, Sheo S.↗

NASA NTRS1987

Evolutionary models of interstellar chemistry

The goal of evolutionary models of interstellar chemistry is to understand how interstellar clouds came to be the way they are, how they will change with time, and to place them in an evolutionary sequence with other celestial objects such as stars. An improved Mark II version of an earlier model of chemistry in dynamically evolving clouds is presented. The Mark II model suggests that the conventional elemental C/O ratio less than one can explain the observed abundances of CI and the nondetection of O2 in dense clouds. Coupled chemical-dynamical models seem to have the potential to generate many observable discriminators of the evolutionary tracks. This is exciting, because, in general, purely dynamical models do not yield enough verifiable discriminators of the predicted tracks.

Prasad, Sheo S.↗

NASA NTRS1987

Chemical evolution of molecular clouds

The principles behind the coupled chemical-dynamical evolution of molecular clouds are described. Particular attention is given to current problems involving the simplest species (i.e., C. CO, O2, and H2) in quiescent clouds. The results of a comparison made between the molecular abundances in the Orion ridge and the hot core (Blake, 1986) are presented.

Prasad, Sheo S.↗