Background Information

                                                                

Alignment vs. Orientation

            We say that molecules are aligned, when they all are along the same axis. Molecules are oriented, when they are along the same axis and point in the same direction.

 

 

Ex: Iodobenzene

 

File:Iodobenzene-3D-vdW.png File:Iodobenzene-3D-vdW.pngFile:Iodobenzene-3D-vdW.png                 File:Iodobenzene-3D-vdW.pngFile:Iodobenzene-3D-vdW.pngFile:Iodobenzene-3D-vdW.png                        File:Iodobenzene-3D-vdW.pngFile:Iodobenzene-3D-vdW.pngFile:Iodobenzene-3D-vdW.png

            Random                                     3-D Aligned                                            Oriented

 

 

 

 

 

Revivals and Molecules

            The Iodobenzene molecules are originally random. To orient the molecules, we send a pump beam into the gas chamber. The pump beam exerts a torque on the molecules, and causes them to rotate. The time it takes for the molecules to return to their original positions, is called the revival time. 

  

P        File:Iodobenzene-3D-vdW.png               After field…   File:Iodobenzene-3D-vdW.png                 Until…      File:Iodobenzene-3D-vdW.png

 

 

    

 

 

Rotational Spectroscopy

Linear Molecules:

An example of a linear molecule is CO, NO, or H2. It is any diatomic molecule which has three moments of inertia (I), two of which are equal to each other and one said to be zero.

 

Symmetric Tops:

Symmetric top molecules can either be oblate or prolate. Oblate symmetric tops have,

 , and are disc shaped. Prolate symmetric tops have, and are roughly football shaped. An example of an oblate symmetric top is benzene, and an example of a prolate symmetric top is chloromethane.

 

Asymmetric tops:

An example of an asymmetric top molecule is water, nitrogen dioxide, and most important for our experiment, Iodobenzene.