Electric resonance method

The electric resonance method (molecular beam electric resonance method) uses three different electric fields. It is time-consuming, however, while it can be used only for simple molecules, it gives very accurate results [3,53], 

---

In addition to moment-of-inertia data, microwave spectra and radiofrequency (AJ — 0, AMj = 1) spectra can be used to measure Stark effects quite accurately. Electric dipole moments good to about 1 % have been calculated from the static, high resolution microwave experiments, and moments with less than 0.01 % error are routinely determined with the electric resonance method. 

Table 8.14. Alkali halides studied by electric resonance methods...

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. 

The first successful application of molecular beam electric resonance to the study of a short-lived free radical was achieved by Meerts and Dymanus [142] in their study of OH. They were also able to report spectra of OD, SH and SD. Their electric resonance instrument was conventional except for a specially designed free radical source, in which OH radicals were produced by mixing H atoms, formed from a microwave discharge in H2, with N02 (or H2S in the case of SH radicals). In table 8.24 we present a complete A-doublet data set for OH, including the sets determined by Meerts and Dymanus, with J = 3/2 to 11/2 for the 2n3/2 state, and 1/2 to 9/2 for the 2ni/2 state. Notice that, for the lowest rotational level (7 = 3/2 in 2n3/2), the accuracy of the data is higher. These transitions were observed by ter Meulen and Dymanus [143], not by electric resonance methods, but by beam maser spectroscopy, with the intention of providing particularly accurate data for astronomical purposes. This is the moment for a small diversion into the world of beam maser spectroscopy. It has been applied to a large number of polyatomic molecules, but apparently OH is the only diatomic molecule to be studied by this method. 

J = 3/2, 5/2 and 7/2 levels of both fine-structure states. Also shown are the /l-doublet transitions observed, first by Dousmanis, Sanders and Townes [4], and subsequently by ter Meulen and Dymanus [165] andMeertsandDymanus [166]. The later studies [166] used molecular beam electric resonance methods which were described in chapter 8, and the most accurate laboratory measurements of transitions within the lowest rotational level were those of ter Meulen and Dymanus [165] using a beam maser spectrometer, also described in chapter 8. In the years following these field-free experiments, attention... 

Using the molecular beam electric resonance method, Bauer and Lew (1 ) measured the transition between the J = 0 and J =... 

More recently, dipole moments have also been calculated from the effect of electric fields on molecular spectra (Stark effect) and from the electric resonance methods applied to molecular beams these are beyond the scope of this book. 

Experimental dipole moments can be obtained in several different ways. The first and most widely used approach is based on the measurement of dielectric constants. The second group of methods utilizes microwave spectroscopy and molecular beams (the Stark effect method, the molecular beam method, the electric resonance method, Raman spectroscopy, etc.). 

The main sources of data are microwave, inlfared and laser induced fluorescence spectroscopy and their related Doppler-free techniques. Results from magnetic and electric resonance methods are also considered. 

---