Magnetic predissociation

Fifjure 7. Circular polarization rate aoatod br- an alignmoni to orientation conversion in laser excited fluorescence of the Tc2 molecule due to magnetic intramolecular interactions and magnetic predissociation. 

The influence of a magnetic field on fluorescence intensity of molecular iodine is the first and perhaps the best understood system. In 1930, Turner proposed that the quenching of the fluorescence of the 811(0,1 ) state in a strong magnetic field is due to an induced predissociation. Later Van Vleck (1932) developed a theory to describe the magnetic predissociation by an induced mixing of the optically excited B state with the dissociative 0 state (Mulliken, 1971). 

Processes (3)-(5) represent spontaneous predissociation, collision-induced (self-) quenching, and magnetic predissociation, respectively. 

The experimental results of Degenkolb et al. are shown in Table 1 together with self-quenching cross sections from other experiments. Their results indicate that the magnetic predissociation rises slowly and falls nearly... 

To explain both the weak natural predissociation and the magnetic predissociation, Vigue et al. (1975) have proposed that these two types of... 

In the following we discuss the general theories of intra- and intermolecular magnetic quenching separately. The theoretical results of intramolecular magnetic quenching will in particular apply to the magnetic predissociation of diatomic molecules (Sections IV and V). 

In Section III we presented a general treatment of intramolecular magnetic quenching in this section we apply the theory to the magnetic predissociation of diatomic molecules. For purposes of comparison, the spontaneous predissociation of diatomic molecules is also discussed in this section. Notice that in this case the final state is in the dissociating (or repulsive) state. 

For the purpose of finding the angular distribution of the products in magnetic predissociation, we choose the Z axis along the magnetic field direction. Here we shall consider only the case in which the magnetic transition moment is along the molecular axis to demonstrate the method of calculation. Other cases can be treated similarly. In this case, Eq. (150) becomes... 

The calculation of the angular distribution of products in magnetic predissociation is similar to that in photodissociation. In the above derivation, we have only demonstrated the calculation of the angular distribution for the case of the magnetic transition moment being along the molecular axis other cases can be treated in a similar manner as those in the photodissociation and will not be discussed here. Notice that when Hfi is independent of / values, Eq. (164) yields P v = 2. 

Magnetic quenching has only begun to attract attention, and most calculations so far are limited to the 12 case. In this section, we discuss the calculation of the magnetic predissociation of the state of I2. 

Since for Ij, the natural predissociation of the state is small, other contributions to the magnetic predissociation discussed in Section III can be ignored. If Jj, can be assumed to be independent of the intermolecular distance (the Condon approximation), Eq. (166) becomes... 

It is commonly believed (Van Vleck, 1932 Chapman and Bunker, 1972 Degenkolb et al, 1969) that the magnetic predissociation of the B state takes place by the process Ou - 0 (AQ = 0). To evaluate the magnetic quenching coefficient V, it is necessary to calculate the electronic matrix element Jo-,o+- Neglecting the mixing due to spin-orbit coupling, the electronic wavefunctions of the Ilo and Ilo- states can be approximately written as (Mulliken, 1971)... 

Auzinsh, M., A.V. Stolyarov, M. Tamanis, and R. Ferber, Magnetic field induced alignment - orientation conversion Non-linear energv shift and predissociation in Tc2 B 1 state, J. Chem. Phys., 105 p. 37 49 (1996). 

The results de scribed in this paper for vdU molecule predissociation demonstrate that the CCCC formalisms provide accurate and efficient methods for the direct prediction of resonance energies and widths of metastable states. In work published elsewhere (36), the CCCC oiethod has also been extended and applied to the first determination of the energies and widths of the autolonlzing resonances of the hydrogen atom in intense magnetic fields. The utility and advantages of the CCCC methods may be sunmarlzed as follows (1) It is an ab initio method (given a defined "exact" hamiltonlan). (2) Only... 

This +M, — M lifetime asymmetry is explained by noting that the B 0+ state could interact with a lu state via both HROT (the —BJ L term) and jjZeeman Thg coupling matrix element is a sum of two terms, one of which depends on the sign of M and the sign of the magnetic field. For +M, the two terms add, whereas for — M, they partially cancel. The fact that the perturber is a repulsive state simply means that the unbound character mixed into the nominal B 0J (v = 40,7 = 77) level is larger for +M than — M. The lifetime difference is responsible for the more rapid nonradiative decay (predissociation) of +M than — M. 

When the predissociation rate is so much larger than the radiative decay rate that the fluorescence quantum yield is too low to measure a radiative decay rate directly, it is possible to infer the decay rate of the parent molecule from the effect of a static magnetic field on the polarization of a photofragment (Buijsse and van der Zande, 1997). 

Laser-induced predissociation in the presence of a surface magnetic field, and dissociation dynamics in the presence of an intense laser field have been treated... 

There exists, in the past few years an increasing interest in the influence of external (magnetic and electric) fields on the dynamics of excited molecular states. This interest is not surprising if we are reminded of the role played by this kind of studies in the development of the atomic physics. We will limit our discussion to the phenomena related to the collisional electronic relaxation application of magnetic fields in the studies of predissociation and of dephasing processes in isolated molecules will not be treated here. 

The iodine molecule has been very thoroughly studied with electric and magnetic level-crossing spectroscopy. The hyperfine structure of the rotational levels affects the profile of the level-crossing curves [849]. A computer fit to the non-Lorentzian superposition of all Hanle curves from the different hfs levels allows simultaneous determination of the Landd factor g and the lifetime t [850]. Because of different predissociation rates the effective lifetimes of different hfs levels differ considerably. 

Stwalley, W.C., Stability of spin-aligned hydrogen at low temperatures and high magnetic fields New field-dependent scattering resonances and predissociations, Phys. Rev. Lett., 37,1628,1976. 

Uang, Y.-H., Ferrante, R.F., and Stwalley, W.C. Model calculations of magnetic-field-induced perturbations and predissociations in Li Li near dissociation, J. Chem. Phys., 74, 6267,1981. 

Feshbach, H., Unified theory of nuclear reactions, Ann. Phys. (NY), 5, 357, 1958. Feshbach, H., A unified theory of nuclear reactions II, Ann. Phys. (NY), 19, 287, 1962. Stwalley, W.C., Stabihty of spin-ahgned hydrogen at low temperatures and high magnetic fields New field-dependent scattering resonances and predissociations, Phys. Rev. Lett., 37, 1628,1976. 

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