Optical Microwave Double Resonance

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,... 

We now describe briefly the FIR laser magnetic resonance studies of the four molecules listed above. FeH has also been studied by mid-infrared laser magnetic resonance, and NiH by microwave/optical double resonance these investigations are discussed elsewhere. 

The NiH radical has been studied quite thoroughly, by FIR laser magnetic resonance as described here [76], but also by microwave/optical double resonance and by mid-... 

The effective Hamiltonian and analysis of the spectra is described in chapter 11 when we discuss the microwave/optical double resonance spectrum. 

Figure 11.1. (a) Principles of the microwave/optical double resonance method, (b) Change of polarisation of fluorescent light resulting from AM= 1 radiofrequency transitions. 

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

Figure 11.10. Principles of microwave/optical double resonance, permitting the observation of rotational transitions in either the ground or excited electronic state [16]. The ground state levels are in thermal equilibrium with the heat bath, and it is assumed that when the molecule in the excited state spontaneously emits a photon, it enters the heat bath rather than returning to the optically-depleted ground state level.

The studies of BaO were important pioneering experiments showing the power of microwave/optical double resonance methods. We shall describe a number of significant applications of these methods later in this chapter. 

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. 

Radiofrequency or microwave/optical double resonance of alkaline earth molecules... 

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 11.21. Energy level diagram and microwave/optical double resonance transitions for the X 2E+ state in SrF and similar systems [38],...

An important development in microwave/optical double resonance, called microwave/optical polarisation spectroscopy, was described by Ernst and Torring [42], The principles of this technique are illustrated in figure 11.22. A linearly polarised probe beam from a tunable laser is sent through the gas sample and a nearly crossed linear polariser, before its final detection. Polarised microwave radiation resonant with a rotational transition in the gas sample is introduced via a microwave horn as shown, and resonant absorption results in a partial change in polarisation of... 

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. 

Figure 11.25. Principles of the microwave/optical double resonance experiment for studying rotational transitions in the ground state of FeO, and the experimental arrangement [49].

Figure 11.27. Microwave/optical double resonance lines observed [48] for the. 1 = 1 6 tran-...

Figure 11.28. Energy level diagram and observed transitions for the microwave/optical double resonance spectrum of CuF. Optical excitation was accomplished using a rhodamine cw dye laser, pumped by an argon ion laser [53],...

TiN has an X 2S+ ground state and rotational transitions in the v = 0 level have been measured and analysed [69, 70] pure millimetre wave and microwave/optical double resonance methods were used, over a frequency range from 37 to 446 GHz. 14N hyperfrne structure was observed for the two lowest rotational transitions, and the spectrum analysed using the conventional effective Hamiltonian, again expressed in cartesian form ... 

Figure 11.35. Top microwave/optical double resonance transitions [71] in MoN (X4 1/2). Bottom microwave/optical double resonance transitions [71] in CrN (X4E 2).

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