Question: In what conditions do some molecules radiate strongly?
About the article "Astronomy", section "Infrared astronomy".

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Infrared astronomy is founded on the detection and analysis of infrared radiation (wavelengths longer than red light).
The infrared spectrum is useful for studying objects that are too cold to radiate visible light, such as planets, circumstellar disks or nebulae whose light is blocked by dust.
Longer infrared wavelengths can penetrate clouds of dust that block visible light, allowing the observation of young stars in molecular clouds and the cores of galaxies.
Observations from the Wide-field Infrared Survey Explorer (WISE) have been particularly effective at unveiling numerous Galactic protostars and their host star clusters.
With the exception of wavelengths close to visible light, infrared radiation is heavily absorbed by the atmosphere, or masked, as the atmosphere itself produces significant infrared emission.
Consequently, infrared observatories have to be located in high, dry places or in space.
Some molecules radiate strongly in the infrared.
This allows the study the chemistry of space; more specifically it can detect water in comets.
Since most structures do not vibrate uniformly (as in the case of the baffled piston), but vibrate according as combinations of flexural, compressional and shear waves.
The radiation characteristics actually depend strongly on whether the bending wave speed is slower than the sound speed in the fluid or faster.
For subsonic bending waves, the radiation is weak, while supersonic bending waves radiate efficiently. 
The following gas phase reaction describes the electron ionization process: formula_1 where M is the analyte molecule being ionized, e− is the electron and M+• is the resulting ion.
In an EI ion source, electrons are produced through thermionic emission by heating a wire filament that has electric current running through it.
The electrons are accelerated to 70 eV in the region between the filament and the entrance to the ion source block.
The accelerated electrons are then concentrated into a beam by being attracted to the trap electrode.
The sample under investigation which contains the neutral molecules is introduced to the ion source in a perpendicular direction to the electron beam.
Close passage of highly energetic electrons, referred to as a "hard" ionization source, causes large fluctuations in the electric field around the neutral molecules and induces ionization and fragmentation.
The radical cation products are then directed towards the mass analyzer by a repeller electrode.
The ionization process often follows predictable cleavage reactions that give rise to fragment ions which, following detection and signal processing, convey structural information about the analyte.
The ionization efficiency and production of fragment ions depends strongly on the chemistry of the analyte and the energy of the electrons.
At low energies (around 20 eV), the interactions between the electrons and the analyte molecules do not transfer enough energy to cause ionization.
At around 70 eV, the de Broglie wavelength of the electrons matches the length of typical bonds in organic molecules (about 0.14 nm) and energy transfer to organic analyte molecules is maximized, leading to the strongest possible ionization and fragmentation.
Under these conditions, about 1 in 1000 analyte molecules in the source are ionized.
At higher energies, the de Broglie wavelength of the electrons becomes smaller than the bond lengths in typical analytes; the molecules then become "transparent" to the electrons and ionization efficiency decreases. 
  Better-than perfect enzymes: Why do some enzymes exhibit faster-than-diffusion kinetics?
See Enzyme kinetics.
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Protein folding problem: Is it possible to predict the secondary, tertiary and quaternary structure of a polypeptide sequence based solely on the sequence and environmental information?
Inverse protein-folding problem: Is it possible to design a polypeptide sequence which will adopt a given structure under certain environmental conditions?
RNA folding problem: Is it possible to accurately predict the secondary, tertiary and quaternary structure of a polyribonucleic acid sequence based on its sequence and environment?
What are the chemical origins of life?
How did non-living chemical compounds generate self-replicating, complex life forms?
Protein design: Is it possible to design highly active enzymes de novo for any desired reaction?
Biosynthesis: Can desired molecules, natural products or otherwise, be produced in high yield through biosynthetic pathway manipulation?  
The infrared part of the electromagnetic spectrum covers the range from roughly 300 GHz (1 mm) to 400 THz (750 nm).
It can be divided into three parts: Far-infrared, from 300 GHz (1 mm) to 30 THz (10 μm).
The lower part of this range may also be called microwaves.
This radiation is typically absorbed by so-called rotational modes in gas-phase molecules, by molecular motions in liquids, and by phonons in solids.
The water in Earth's atmosphere absorbs so strongly in this range that it renders the atmosphere in effect opaque.
However, there are certain wavelength ranges ("windows") within the opaque range that allow partial transmission, and can be used for astronomy.
The wavelength range from approximately 200 μm up to a few mm is often referred to as "sub-millimeter" in astronomy, reserving far infrared for wavelengths below 200 μm.
Mid-infrared, from 30 to 120 THz (10 to 2.5 μm).
Hot objects (black-body radiators) can radiate strongly in this range, and human skin at normal body temperature radiates strongly at the lower end of this region.
This radiation is absorbed by molecular vibrations, where the different atoms in a molecule vibrate around their equilibrium positions.
This range is sometimes called the "fingerprint region", since the mid-infrared absorption spectrum of a compound is very specific for that compound.
Near-infrared, from 120 to 400 THz (2,500 to 750 nm).
Physical processes that are relevant for this range are similar to those for visible light.
The highest frequences in this region can be detected directly by some types of photographic film, and by many types of solid state image sensors for infrared photography and videography.