Such as neutrons electrons or high energy x rays

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such as neutrons, electrons, or high energy X-rays interact with a regulararrangement of molecules (as in a crystal).Microwave spectroscopy commonly measures changes in the rotation of molecules,and can be used to identify molecules in outer space. Infrared spectroscopymeasures the vibration of molecules, including stretching, bending or twistingmotions. It is commonly used to identify the kinds of bonds or functional groupsin molecules. Changes in the arrangements of electrons yield absorption oremission lines in ultraviolet, visible or near infrared light, and result incolour. Nuclear resonance spectroscopy measures the environment of particularnuclei in the molecule, and can be used to characterise the numbers of atoms indifferent positions in a molecule.Theoretical aspectsThe study of molecules by molecular physics and theoretical chemistry is largelybased on quantum mechanics and is essential for the understanding of thechemical bond. The simplest of molecules is the hydrogen molecule-ion, H2+, and
the simplest of all the chemical bonds is the one-electron bond. H2+ is composedof two positively charged protons and one negatively charged electron, whichmeans that the Schrödinger equation for the system can be solved more easily dueto the lack of electron–electron repulsion. With the development of fast digitalcomputers, approximate solutions for more complicated molecules became possibleand are one of the main aspects of computational chemistry.When trying to define rigorously whether an arrangement of atoms is sufficientlystable to be considered a molecule, IUPAC suggests that it "must correspond to adepression on the potential energy surface that is deep enough to confine atleast one vibrational state".[4] This definition does not depend on the natureof the interaction between the atoms, but only on the strength of theinteraction. In fact, it includes weakly bound species that would nottraditionally be considered molecules, such as the helium dimer, He2, which hasone vibrational bound state[27] and is so loosely bound that it is only likelyto be observed at very low temperatures.Whether or not an arrangement of atoms is sufficiently stable to be considered amolecule is inherently an operational definition. Philosophically, therefore, amolecule is not a fundamental entity (in contrast, for instance, to anelementary particle); rather, the concept of a molecule is the chemist's way ofmaking a useful statement about the strengths of atomic-scale interactions inthe world that we observe.See alsoAtomChemical polarityCovalent bondDiatomic moleculeList of compoundsList of interstellar and circumstellar moleculesMolecular biologyMolecular design softwareMolecular engineeringMolecular geometryMolecular HamiltonianMolecular ionMolecular modellingMolecular promiscuityMolecular orbitalNon-covalent bondingPeriodic systems of small moleculesSmall moleculeComparison of software for molecular mechanics modelingVan der Waals moleculeWorld Wide Molecular MatrixPapapishu-Lab-icon-6.svgChemistry portalIssoria lathonia.jpgBiology

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