Theoretical Study On The Orientation Of Cold Polar Molecules In An Electric Field

The external electrostatic field control and measurement of molecular orientation is important in the modern atomic, molecular and optical (AMO) physics. Molecular orientation plays an important role in a variety of fields ranging from molecular reaction dynamics, stereo dynamics, to quantum computing and information, etc. Theoretic studies in this field have been developed rapidly in the recently years.We chose the symmetric top molecules cooled in supersonic expansions as the candidate. This paper describes the orientation theory of cold polar molecules in an electrostatic field. Using a rigid rotor model, based on a theoretical description of the interaction of molecular dipole moment with the external electric field, a theoretical study on orientation of polar molecules in the strong external field is presented.The high field can hybridize the free rotate states of polar molecules, to produce the pendular states. The exact matrix diagonalization method becomes an important research tool of theoretic studies. This method is based on a commutation from free field states to pendular states. By diagonalizing the Hamiltonian matrix, the Schrodinger equation is solved to obtain the pendular eigenvalues and the corresponding pendular eigenstates. Then we can measure optical spectrum of pendular state, and calculate the orientation probability and the molecular steric distribution.Because the pendular eigenstate is the linear combination of the free field states, and the pendular eigenvalues are difficult to be labeled, the exact matrix diagonalization only use on observe the numerical outputting. The paper resolve this problem and obtain the physical significance of the pendulum。Therefore, the orientation theory will have unique properties and great potential, which is the focus of this thesis.