Molecular beam electrical resonance

Figure Cl.3.1. Schematic diagram of a molecular beam electric resonance spectrometer. (Taken from [60].)...

In dimers composed of equal molecules the dimer components can replace each other through tunneling. This effect has been discovered by Dyke et al. [1972] as interconversion splitting of rotational levels of (HF)2 in molecular beam electric resonance spectra. This dimer has been studied in many papers by microwave and far infrared tunable difference-frequency laser spectroscopy (see review papers by Truhlar [1990] and by Quack and Suhm [1991]). The dimer consists of two inequivalent HE molecules, the H atom of one of them participating in the hydrogen bond between the fluorine atoms (fig. 60). PES is a function of six variables indicated in this figure. 

Dyke, T.R., Mack, K.M. and Muenter, J.S. (1977) The structure of water dimer from molecular beam electric resonance spectroscopy, J. Chem. Phys., 66,498-510. 

Other measurements. Induced dipole moments can be measured by most of the familiar methods that are designed to measure permanent dipole moments. We mention in particular the beam deflection method by electric fields, using van der Waals molecules, and molecular beam electric resonance spectroscopy of van der Waals molecules [373, 193, 98]. 

The interpretation of the microwave spectra recorded in the molecular beam electric resonance experiments shows that the dipole moment increases on complex... 

Fig. 2. J = 1, Mj = 0- 1 molecular beam electric resonance for (H20)2 at an electric field strength of 599.50V/cm. The triplet nuclear spin state gives rise to the four spin-spin components of this transition. (Reproduced from Ref.

Nuclear hyperfine splittings in the rotational spectra of dimers have been observed in the molecular beam electric resonance experiments and the Fourier transform microwave experiments. In most cases, the coupling constants are interpreted with the simplified expression given in Eqn. (6) for axially symmetric molecules in the K=0 rotational manifold. Thus both the nuclear quadrupole coupling term and the... 

As with the Zeeman interaction discussed earlier, (1.43) is usually contracted to the space-fixed p = 0 component. An extremely important difference, however, is that in contrast to the nuclear spin Zeeman effect, the Stark effect in a 1Z state is second-order, which means that the electric field mixes different rotational levels. This aspect is thoroughly discussed in the second half of chapter 8 the second-order Stark effect is the engine of molecular beam electric resonance studies, and the spectra, such as that of CsF discussed earlier, are usually recorded in the presence of an applied electric field. 

Molecular beam electric resonance of closed shell molecules [1 463... 

As the name suggests, electric resonance experiments make use of electric fields to achieve molecular state selection. Figure 8.25 shows a schematic diagram of a molecular beam electric resonance instrument, which we will discuss in more detail when we describe experiments on the CsF molecule. In contrast to the magnetic resonance apparatus discussed earlier, the A, B and C fields in figure 8.25 are all electric fields. In... 

Several other alkali fluorides have been studied by molecular beam electric resonance. The analyses are similar to that described above and similar sets of molecular constants have been determined the molecules studied include 85Rb19F and 87Rb19F [56], 39K19F [57], 23Na19F [58, 59] and 7Li19F [60, 61]. 

Figure 8.33. Block diagram of the molecular beam electric resonance instrument used by Freund, Fisk, Flerschbach and Klemperer [55]. Transitions induced in the C field region which obey the selection rule AM = 1 result in an increase in the number of molecules reaching the detector this is the flop-in mode of detection.

The alkali halide molecules have been studied comprehensively by molecular beam electric resonance methods. Table 8.14 presents a summary with references. In most cases the electric quadrupole coupling constants have been determined, and usually also the nuclear spin-rotation constants. 

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