The various levels of photodissociation cross sections

For most small systems the chemical and electronic channels are rather obvious and therefore the labels 7 and e will be omitted hereafter. Normally, one measures integral absorption cross sections, 

In the following we will call the a u,n,j) partial photodissociation cross sections.t They are the cross sections for absorbing a photon with frequency u and producing the diatomic fragment in a particular vibrational-rotational state (n,j). Partial dissociation cross sections for several photolysis frequencies constitute the main body of experimental data and the comparison with theoretical results is based mainly on them. Summation over all product channels (n,j) yields the total photodissociation cross section or absorption cross section  

The product state distributions, which we shall amply discuss in this monograph, are defined by 

The confluence of theory and experiment achieved in recent years has greatly deepened our understanding of molecular photodissociation. At this point, however, it is important to underline that the cornerstone of realistic dynamical investigations is a multi-dimensional potential energy surface (PES). The interrelation between PESs on one hand and the various dissociation cross sections on the other hand is one prominent topic of this book and therefore we think it is useful to elucidate some qualitative aspects of PESs before we start with the development of the dynamical concepts. 

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