Double resonance studies

Riedel A, S Fetzner, M Rampp, F Lingens, U Liebl, J-L Zrmmermann, W Nitschke (1995) EPR, electron spin echo envelope modulation, and electron nuclear double resonance studies of the 2Ee-2S centers of the 2-halobenzoate 1,2-dioxygenase from Burkholderia (Pseudomonas) cepacia 2CBS. J Biol Chem 270 30869-30873. 

Mukai, K. Tsuzuki, N. Ishizu, K. Ouchi, S. Fukuzawa K Electron nuclear double resonance studies of radicals produced by the Pb02 oxidation of a-tocopherol and its model compound in solution. Chem. Phys. Lipids 1981, 29, 129-135. 

ENDOR (electron nuclear double resonance) studies of diphenyl-carbene indicated a dihedral angle of 34° for this species >. 

S2 - Sq fluorescence and radiationless transitions from the state of porphyrins have been studied in order to reveal photodynaunics of porphyrins. The S2 state fluorescence of zinc(II)-tetraphenylporphin is caused even by the excitation to the state. Two-photon absorption and optical-optical double resonance studies show that a stepwise two-photon absorption through the state is a main process populating the S2 state. 

Electron-nuclear double-resonance studies aconitase, 38 326-328 [4Fe0134S] cluster, 38 355-358 Electron paramagnetic resonance carbon monoxide oxidoreductase, 32 326-328... 

Nelson WH, Sagstuen E, Hole EO, Close DM (1998) Electron spin resonance and electron nuclear double resonance study of X-irradiated deoxyadenosine proton transfer behaviour of primary ionic radicals. Radiat Res 149 75-86... 

German, K.R., Bergman, T.H., Weinstock, E.M. and Zare, R.N. (1973). Zero-field level crossing and optical radio-frequency double resonance studies of the A2E+ states of OH and OD, J. Chem. Phys., 58, 4304-4318. 

This book is concerned primarily with the rotational levels of diatomic molecules. The spectroscopic transitions described arise either from transitions between different rotational levels, usually adjacent rotational levels, or from transitions between the fine or hyperfine components of a single rotational level. The electronic and vibrational quantum numbers play a different role. In the majority of cases the rotational levels studied belong to the lowest vibrational level of the ground electronic state. The detailed nature of the rotational levels, and the transitions between them, depends critically upon the type of electronic state involved. Consequently we will be deeply concerned with the many different types of electronic state which arise for diatomic molecules, and the molecular interactions which determine the nature and structure of the rotational levels. We will not, in general, be concerned with transitions between different electronic states, except for the double resonance studies described in the final chapter. The vibrational states of diatomic molecules are, in a sense, relatively uninteresting. 

In this book, which is concerned predominantly with rotational transitions and their fine and hyperfine structure, we will have only a peripheral interest in the details of vibrational structure. Similarly we will not usually be concerned directly with electronic transitions, except in double resonance studies. Nevertheless it is important to see the broader picture, in order to understand better the detailed structure. 

In this chapter we are concerned with the excited triplet states. The c 3 nu state is the subject of this section, whilst the d and k 3nu states will appear later when we discuss microwave/optical double resonance studies. These triplet states are metastable,... 

Figure 8.16 shows that the next excited 3nu state of H2 is the d state. This has been studied by means of some elegant double resonance studies, which are described in detail in chapter 11. 

Finally, there are numerical relationships between groups of transitions which share common levels these relationships correspond to combination differences in other branches of spectroscopy. Through a combination of these relationships, double resonance studies and Zeeman effect measurements, it was possible to establish the energy level diagram shown in figure 10.74. Each level is characterised by its parity and J value the observed transitions are also shown in figure 10.74. The important task... 

We have, we hope, provided enough detail about the Zeeman effect to show how almost every microwave resonance could be assigned, so far as the J values were concerned. A final remark should be made concerning the parity labels. These depend upon the identification of a J = 1 /2 <- 1/2 transition, and the measured g-factors for the two J = 1/2 levels which identify their e//, and hence total parities. The parities of all other levels then follow because all transitions are electric-dipole allowed, between states of opposite parity. As we have mentioned earlier, the combination of numerical relationships between the resonance frequencies, double resonance studies, and Zeeman effect measurements enabled the pattern of levels lying within 8 cm 1 of the dissociation limit to be established. The highest level, J = 7/2 (—parity), in figure 10.74, was thought to lie within 20 MHz (<0.001 cm-1) of the dissociation limit. 

Before commencing our description of true double resonance studies of molecular systems, we describe an extremely important precursor study of the CN radical, which pointed the way to many later experiments. 

The first radiofrequency/optical double resonance studies of molecules were published almost simultaneously. Observations of OH and OD were described by German and Zare [10] late in 1969, and will be discussed in detail in the next subsection. A few months later studies of the CS molecule in its excited A 1 n were reported by Silvers, Bergeman and Klemperer [11], with more detailed results described later by Field and Bergeman [12], We now describe these investigations, which are in some ways simpler than those of OH because of the absence of electron and nuclear spin effects in the CS 1n state. 

Figure 11.5. Ground and excited state levels involved in the radiofrequency/optical double resonance study of CS in its A 1 n state [12].

Early radiofrequency or microwave/optical double resonance studies [1 877... 

The first observation of a rotational transition in a diatomic molecule in a short-lived, excited electronic state, namely BaO, was reported by Field, Bradford, Broida and Harris [14]. This work followed earlier double resonance studies by Field, Bradford, Harris and Broida [15] in which rotational transitions in the ground state of BaO were detected. A more comprehensive investigation of both ground and excited state rotational transitions in BaO was described by Field, English, Tanaka, Harris and Jennings [16] we now review this work. 

In chapter 8 we described the elegant studies of Lichten [18] on the electronically excited c 3nu state of H2. Lichten s experiments involved electronic excitation of a beam of H2 molecules by collision with an electron beam, but they were not double resonance experiments. Rather, they were classic molecular beam magnetic resonance studies of the type described extensively in chapter 8. In this section we discuss later experiments on H2, again electronically excited by collision with electrons, but involving microwave/optical double resonance studies. Before we describe these experiments, however, we summarise the relevant excited states of H2, repeating to some extent our discussion in chapter 8. 

Microwave/optical double resonance studies have been described for SrF by Domaille, Steimle and Harris [38], for CaCl by Domaille, Steimle and Harris [39], and for CaF by... 

Figure 11.24. Experimental arrangement used by Ernst and Kindt [44] in their pump/probe microwave/optical double resonance study of a rotational transition (18.2 GHz) in the ground state of CaCl. The photomultiplier tubes which monitor fluorescence are situated on the axis perpendicular to both the laser beam and the molecular beam. The C region, where the molecular beam is exposed to microwave radiation, is magnetically shielded to minimise stray Zeeman effects. The microwave power was amplitude modulated at 160 Hz and the modulated fluorescence detected by photomultiplier B. 

Within the = 4 fine-structure component, ten rotational transitions were observed in the double resonance studies, with J values ranging from 4 to 14, as shown... 

The values of the molecular parameters (in MHz) obtained from a combination of the pure microwave and double resonance studies were as follows ... 

All of the other required matrix elements have been given elsewhere [77] some of the constants in equation (11.51) were determined in the laser magnetic resonance study, and the remaining constants were obtained from the double resonance study. The final parameters for the 0 = 0 level were (in MHz) as follows ... 

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