Crossed molecular beam

Molecular beam method is a method of chemistry, can be obtained with the kinetic and structural information on chemical reactions.

Principle

It produces at least two beams ( molecular beams or atomic beams ) each consisting of a type particles. By crosses and combining these beams in a vacuum, the molecules are reacted.

Here, speed and collision of molecular beams lead to a certain scattering of:

• Reactants
• Reaction end products
• Intermediates

The vacuum prevents an influence by " foreign " molecules,

• That could distract the molecular beams and products,
• Which could undesirably participate in the reaction.

These " foreign " molecules are in reactions under normal laboratory conditions of molecules of the solvent, the air, and possibly of a protective gas.

The detection can be done with mass spectrometry for kinetic information, or with the rotation spectroscopy, infrared spectroscopy for structural information.

Kinetic studies

In the kinetics of the molecular beam method is used to explore the impact of the processes involved in a reaction, atoms and molecules without disturbing intermolecular interactions. The interpretation of the shock processes provides statistical information, in particular to the minimum energy required for the reaction. Not every collision apparently reactive particles ends in a reaction of these particles.

The molecular beams are crossed, the molecules react in the crossover region partially with each other. Through collision and partial reaction occurs scattering of molecules. The scattered molecules are detected, determine their mass and from the composition of the scattered particles is determined.

The following phenomena occur:

• Molecules that do not collide in the intersection area retain the flight direction of the original molecular beam.

• Molecules collide and react mainly take a flight direction, which results from the flight directions of the original molecular beams.

• Molecules, but the conflict does not respond, are strongly scattered in all directions.

The deviation from the angle of the original flight direction by collision or reaction, the scattering angle of the reaction products, the size of the crossover region of the molecular beam, and the flight time of the particles can be evaluated on the basis of simple collision theory and refined collision theory.

Structural studies

For structural studies, the collisions are less interesting. Here structures of intermediates and final products of reactions to be investigated.

It can be measured only particles that react that occupy so more or less the direction of flight, the results from the flight directions of the original molecular beams.

With the microwave spectroscopy and infrared spectroscopy, sometimes by means of other spectroscopic methods, one attains information about bond lengths, rotations, conformation, vibration, etc., which occur in the intermediates and final products and may from the structure and the bonding state in otherwise poorly accessible species suggest.

Application

The molecular beam method is widely used for a variety of kinetic studies in physical chemistry. Structural analysis with the molecular beam method is nowadays increasingly being used in the study of "exotic " complexes, for example of mercury -noble gas complexes.

Both types of applications are used more basic research and are therefore hardly used industrially.