Molecular inelastic

B.S. Hudson, A. Warshel R.G. Gordon (1974). J. Chem. Phys., 61, 2929-2939. Molecular inelastic neutron scattering computational methods using consistent force fields. 

Molecular projectiles offer the possibility of additional direct inelastic channels, namely, the excitation or de-excitation of the molecular internal modes, much as for gas-phase molecular inelastic scattering. Unlike a gas-phase collision of a molecule with a structureless projectile, here the energy balance of the internal modes of the molecule need not be met entirely by the translation. The participation of the surface degrees of freedom is possible and the low-energy modes of the surface, not only phonons but also electron-hole pairs, are particularly important in bridging the gap (remember the exponential gap principle) and thereby making such inelastic collisions quite efficient. 

Radiation probes such as neutrons, x-rays and visible light are used to see the structure of physical systems tlirough elastic scattering experunents. Inelastic scattering experiments measure both the structural and dynamical correlations that exist in a physical system. For a system which is in thennodynamic equilibrium, the molecular dynamics create spatio-temporal correlations which are the manifestation of themial fluctuations around the equilibrium state. For a condensed phase system, dynamical correlations are intimately linked to its structure. For systems in equilibrium, linear response tiieory is an appropriate framework to use to inquire on the spatio-temporal correlations resulting from thennodynamic fluctuations. Appropriate response and correlation functions emerge naturally in this framework, and the role of theory is to understand these correlation fiinctions from first principles. This is the subject of section A3.3.2. 

Lykke K R and Kay B D 1990 State-to-state inelastic and reactive molecular beam scattering from surfaces Laser Photoionization and Desorption Surface Analysis Techniquesvo 1208, ed N S Nogar (Bellingham, WA SPIE) p 1218... 

Vibrational spectroscopy provides detailed infonnation on both structure and dynamics of molecular species. Infrared (IR) and Raman spectroscopy are the most connnonly used methods, and will be covered in detail in this chapter. There exist other methods to obtain vibrational spectra, but those are somewhat more specialized and used less often. They are discussed in other chapters, and include inelastic neutron scattering (INS), helium atom scattering, electron energy loss spectroscopy (EELS), photoelectron spectroscopy, among others. 

Although inelastic X-ray scattering holds promise for the investigation of biological molecular dynamics, it is still in its infancy, so in the subsequent discussion X-ray scattering is examined only in the case in which inelastic and elastic scattering are indistinguishable experimentally. 

A type of molecular resonance scattering can also occur from the formation of short-lived negative ions due to electron capture by molecules on surfrices. While this is frequently observed for molecules in the gas phase, it is not so important for chemisorbed molecules on metal surfaces because of extremely rapid quenching (electron transfer to the substrate) of the negative ion. Observations have been made for this scattering mechanism in several chemisorbed systems and in phys-isorbed layers, with the effects usually observed as smaU deviations of the cross section for inelastic scattering from that predicted from dipole scattering theory. 

Inelastic deformation can cause product failure arising out of a massive realignment of the plastic s molecular structure. A product undergoing inelastic deformation does not return to its original state when its load is removed. It should be remembered that there are plastics that are sensitive to this situation and others that are not. 

Pack R. T. Relation between some exponential approximations in rotationally inelastic molecular collisions, Chem. Phys. I ett. 14, 393-5 (1972). 

Here we shall be concerned with the interaction of inacming diatomic molecules (H-/ 0.) with either types of potential energy wells The molecular InteractJjon (responsible for elastic and direct-inelastic scattering with extremely short residence times of the irpinglng molecules in the potential) and the chemisorptive interaction (leading to dissociative adsorption and associative desorption, reflectively, and associated with H (D) atoms trapped in the chemisorption potential for an appreci le time). 

---