THE PHOTOLYSIS OF KETENE AT LOW TEMPERATURES

1957 ◽  
Vol 35 (10) ◽  
pp. 1137-1138 ◽  
Author(s):  
W. G. Paterson ◽  
H. Gesser
Keyword(s):  
Carbon Monoxide ◽  
Quantum Yield ◽  
Low Temperature ◽  
Low Temperatures ◽  
Photochemical Decomposition

The photochemical decomposition of ketene at 2700 Å has been investigated at −78 °C. The quantum yield of carbon monoxide is two, indicating that the recombination of methylene radicals does not occur at this low temperature.

The photochemical and thermal decompositions of hydrogen sulphide

1953 ◽  
Vol 216 (1126) ◽  
pp. 344-361 ◽  
Keyword(s):  
Thermal Decomposition ◽  
Quantum Yield ◽  
Hydrogen Sulphide ◽  
Low Temperatures ◽  
Room Temperature ◽  
Large Fraction ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Photochemical Decomposition ◽  
Bimolecular Mechanism

The photochemical decomposition of hydrogen sulphide has been investigated at pressures between 8 and 550 mm of mercury and at temperatures between 27 and 650° C, using the narrow cadmium line ( λ 2288) and the broad mercury band (about λ 2550). At room temperature the quantum yield increases with pressure from 1.09 at 30 mm to 1.26 at 200 mm. Above 200 mm pressure there was no further increase in the quantum yield. Temperature had little effect on the quantum yield at λ 2550, but there was a marked increase in the rate of hydrogen production between 500 and 650° C with 2288 Å radiation. This may have been caused by the decomposition of excited hydrosulphide radicals. The results are consistent with a mechanism involving hydrogen atoms and hydrosulphide radicals. The mercury-photosensitized reaction is less efficient than the photochemical decomposition, the quantum yield being only about 0.45. The efficiency increased with temperature and approached unity at high temperatures and pressures. This agrees with the suggestion that a large fraction of the quenching collisions lead to the formation of Hg ( 3 P 0 ) atoms. The thermal decomposition is heterogeneous at low temperatures and becomes homogeneous and of the second order at 650° C. The experimental evidence suggests the bimolecular mechanism 2H 2 S → 2H 2 + S 2 . The activation energies are 25 kcal/mole (heterogeneous) and 50 kcal/mole (homogeneous).

Mechanism of the Direct Photochemical Decomposition of Thietane and its Derivatives in the Vapor Phase, in Solution, and in Glassy Matrices

1975 ◽  
Vol 53 (12) ◽  
pp. 1744-1755 ◽  
Author(s):  
David R. Dice ◽  
Ronald P. Steer
Keyword(s):  
Low Temperature ◽  
Gas Phase ◽  
Vapor Phase ◽  
Low Temperatures ◽  
Condensed Media ◽  
Photochemical Decomposition ◽  
Glassy Matrices

The direct photolyses of thietane, 3-ethyl-2-propylthietane, and 3-methylthietane in the vapor phase, in solution, and in glassy matrices at low temperatures have been examined. The effects of varying the photolysis wavelength, the temperature, the pressure and the phase of the substrate, and of adding inert thermalizers on the nature and yields of the various products have been measured. The results are interpreted in terms of initial C—S cleavage to give a 1,4-biradical which may, in the gas phase, decompose or ring close before complete equilibration of the various rotamers is achieved, or which may be thermalized in condensed media and trapped in glassy matrices at low temperature.

In situ Tensile Experiments at Low Temperatures on Niobium Single Crystals by H.V.E.M.

1975 ◽  
Vol 33 ◽  
pp. 58-59
Author(s):  
F. H. Louchet ◽  
L. P. Kubin
Keyword(s):  
Electron Microscope ◽  
Transition Temperature ◽  
Low Temperature ◽  
Slip System ◽  
Low Temperatures ◽  
Tensile Axis ◽  
Image Intensifier ◽  
Screw Dislocations ◽  
Source Operation

Experiments have been carried out on the 3 MeV electron microscope in Toulouse. The low temperature straining holder has been previously described Images given by an image intensifier are recorded on magnetic tape.The microtensile niobium samples are cut in a plane with the two operative slip directions [111] and lying in the foil plane. The tensile axis is near [011].Our results concern:- The transition temperature of niobium near 220 K: at this temperature and below an increasing difference appears between the mobilities of the screw and edge portions of dislocations loops. Source operation and interactions between screw dislocations of different slip system have been recorded.

INVAR M93

Alloy Digest ◽  
2008 ◽  
Vol 57 (1) ◽  
Keyword(s):  
Fracture Toughness ◽  
Low Temperature ◽  
Physical Properties ◽  
Tensile Properties ◽  
Low Temperatures ◽  
Bend Strength ◽  
Temperature Performance ◽  
Ni Content ◽  
Precision Alloys ◽  
Ni Alloy

Abstract Invar is an Fe-Ni alloy with 36% Ni content that exhibits the lowest expansion of known metals from very low temperatures up to approximately 230 deg C (445 deg F). Invar M93 is a cryogenic Invar with improved weldability. This datasheet provides information on composition, physical properties, hardness, elasticity, tensile properties, and shear and bend strength as well as fracture toughness and fatigue. It also includes information on low temperature performance as well as forming and joining. Filing Code: FE-143. Producer or source: Metalimphy Precision Alloys.

Low-Temperature Study of the Iron-Mediated [4 + 1] Cyclization of Allenyl Ketones with Carbon Monoxide

1996 ◽  
Vol 15 (12) ◽  
pp. 2829-2832 ◽  
Author(s):  
Matthew S. Sigman ◽  
Bruce E. Eaton ◽  
Jerald D. Heise ◽  
Clifford P. Kubiak
Keyword(s):  
Carbon Monoxide ◽  
Low Temperature ◽  
Temperature Study

FEC-LiTFSI-Pyr1ATFSI Ionic Liquid Electrolyte to Improve Low Temperature Performance of Lithium-Ion Batteries

2014 ◽  
Vol 986-987 ◽  
pp. 80-83
Author(s):  
Xiao Xue Zhang ◽  
Zhen Feng Wang ◽  
Cui Hua Li ◽  
Jian Hong Liu ◽  
Qian Ling Zhang
Keyword(s):  
Low Temperature ◽  
Lithium Ion Batteries ◽  
Low Temperatures ◽  
Freezing Point ◽  
Lithium Ion ◽  
Liquid Electrolyte ◽  
Capacity Retention ◽  
Composite Electrolyte ◽  
Ionic Liquid Electrolyte ◽  
Fluoroethylene Carbonate

N-methyl-N-allylpyrrolidinium bis (trifluoromethanesulfonyl) imide (PYR1ATFSI) with substantial supercooling behavior is synthesized to develop low temperature electrolyte for lithium-ion batteries. Additive fluoroethylene carbonate (FEC) in LiTFSI/PYR1ATFSI/EC/PC/EMC is found that it can reduce the freezing point. LiFePO4/Li coin cells with the FEC-PYR1ATFSI electrolyte exhibit good capacity retention, reversible cycling behavior at low temperatures. The good performance can be attributed to the decrease in the freezing point and the polarization of the composite electrolyte.

Anthracene fluorescence at low temperatures. I. Purified single crystals

1972 ◽  
Vol 25 (7) ◽  
pp. 1411 ◽  
Author(s):  
LE Lyons ◽  
LJ Warren
Keyword(s):  
Low Temperature ◽  
Single Crystals ◽  
Fluorescence Spectrum ◽  
Low Temperatures ◽  
Free Exciton ◽  
Deformation Bands ◽  
Exciton Emission ◽  
Polarized Emission ◽  
Impurity Bands ◽  
Phonon Structure

The low-temperature fluorescence spectrum of purified vapour-grown anthracene single crystals is presented and the free-exciton emission distinguished from a number of defect or impurity bands present even in the purest crystals. In assigning the observed bands the symmetry of the active vibrations and the origin of background fluorescence and deformation bands are discussed. The phonon structure in the region of the fluorescence origin was found to be almost completely b-polarized. Emission of electronic origin (25103 cm-1) was too weak to be observed. Polarization ratios of the principal vibronio bands at 5.6 K are given.

Desiccation and low temperature attenuate the effect of UVC254 nm in the photobiont of the astrobiologically relevant lichens Circinaria gyrosa and Buellia frigida

2014 ◽  
Vol 14 (3) ◽  
pp. 479-488 ◽  
Author(s):  
T. Backhaus ◽  
R. de la Torre ◽  
K. Lyhme ◽  
J.-P. de Vera ◽  
J. Meeßen
Keyword(s):  
Low Temperature ◽  
Low Temperatures ◽  
Photosynthetic Activity ◽  
Real Space ◽  
Fast Recovery ◽  
Protective Mechanisms ◽  
Subzero Temperatures ◽  
High Viability ◽  
Buellia Frigida ◽  
Insight Into

AbstractSeveral investigations on lichen photobionts (PBs) after exposure to simulated or real-space parameters consistently reported high viability and recovery of photosynthetic activity. These studies focused on PBs within lichen thalli, mostly exposed in a metabolically inactive state. In contrast, a recent study exposed isolated and metabolically active PBs to the non-terrestrial stressor UVC254 nm and found strong impairment of photosynthetic activity and photo-protective mechanisms (Meeßen et al. in 2014b). Under space and Mars conditions, UVC is accompanied by other stressors as extreme desiccation and low temperatures. The present study exposed the PBs of Buellia frigida and Circinaria gyrosa, to UVC in combination with desiccation and subzero temperatures to gain better insight into the combined stressors' effect and the PBs' inherent potential of resistance. These effects were examined by chlorophyll a fluorescence which is a good indicator of photosynthetic activity (Lüttge & Büdel in 2010) and widely used to test the viability of PBs after (simulated) space exposure. The present results reveal fast recovery of photosynthetic activity after desiccation and subzero temperatures. Moreover, they demonstrate that desiccation and cold confer an additional protective effect on the investigated PBs and attenuate the PBs' reaction to another stressor – even if it is a non-terrestrial one such as UVC. Besides other protective mechanisms (anhydrobiosis, morphological–anatomical traits and secondary lichen compounds), these findings may help to explain the high resistance of lichens observed in astrobiological studies.

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