Optical probes of atomic and molecular decay processes.

Conference · Sat Jan 01 04:00:00 EST 2005

OSTI ID:1007387

Pratt, S T ^[1]

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1. Chemistry

The study of molecular photoionization and photodissociation dynamics provides insight into the intramolecular mechanisms by which energy and angular momentum are exchanged and redistributed among the internal degrees of freedom of highly excited molecules and, more specifically, into the mechanisms that determine the decay pathways and resulting product-state distributions for the excited molecules. These mechanisms lie at the heart of one of the principal subjects of chemistry, that is, understanding and controlling the factors that govern the making and breaking of chemical bonds. The objective of this experimental research program is to elucidate these fundamental mechanisms and to provide useful prototypes for the development of a general qualitative understanding of their ramifications. In this program, the primary focus is on resonant processes in the ionization and dissociation continua, that is, on autoionization and predissociation. These processes are studied as a function of the electronic, vibrational, and rotational quantum numbers of the resonances, allowing a better understanding of their fundamental mechanisms. In the past three years, the primary emphasis of this experimental program has been on understanding the process of vibrational autoionization in Rydberg states of small polyatomic molecules. Vibrational autoionization corresponds to the decay of resonances above the ionization threshold into the continuum through the conversion of vibrational energy into electronic/translational energy of the highly excited/ejected electron. For example, at sufficiently high principal quantum number, the members of a Rydberg series converging to the v{sup +} = 1 level of the NO{sup +} X {sup 1}{Sigma}{sup +} state lie energetically above the v{sup +} = 0 ionization threshold. As a result, these series members can undergo vibrational autoionization into the X {sup 1}{Sigma}{sup +}, v{sup +} = 0 continuum. This process can be understood as the bound Rydberg electron undergoing a vibrationally superelastic collision with the ion core, with the electron attaining sufficient energy to escape into the continuum. Thus, vibrational autoionization provides a simple example of the coupling between the nuclear and electronic degrees of freedom in molecules, and can be used to provide insight into much more complicated systems. In polyatomic molecules, I am particularly interested in determining how this process depends on both the specific normal vibrational modes involved in the process and the electronic character of the resonances.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: SC
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1007387
• Report Number(s): ANL/CHM/CP-116022
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ANGULAR MOMENTUM
AUTOIONIZATION
CHEMICAL BONDS
DEGREES OF FREEDOM
NITRIC OXIDE
PHOTOIONIZATION
PREDISSOCIATION
QUANTUM NUMBERS
RYDBERG STATES
VIBRATIONAL STATES