Permanent moments molecular beams

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 difficulty In distinguishing permanent dipole from Induced dipole moment effects In a molecular beam deflection... 

Steimle and coworkers [95Ste2] have previously determined the permanent electric dipole moments of PtC in two electronic states using molecular beam optical Stark spectroscopy (/<(X E = 0.99(5), fi A 11) = 2.454(3), in Debye units). More recently, the dipole moments of two further states and an unexpeetedly large nuclear-spin magnetie rotation splitting were determined as follows ([99Bea], molecular beam LIF) ... 

The Rabi technique of radio frequency or microwave spectroscopy in atomic or molecular beams [10.14-10.17] has made outstanding contributions to the accurate determination of ground state parameters, such as the hfs splittings in atoms and molecules, small Coriolis splitting in rotating and vibrating molecules, or the narrow rotational structures of weakly bound van der Waals complexes [10.18]. Its basic principle is illustrated in Fig. 10.9. A collimated beam of molecules with a permanent dipole moment is deflected in a static... 

The diatomic yttrium halides have been the topic of both ab initio and experimental studies. Fischell et al. (1980) have studied the excitation spectra of the YCl diatomic molecule using the laser-induced fluorescence (LIF) method. More recently, Xin et al. (1991) have studied the B ri-X system of YCl in high resolution. The rotational analysis of the observed bands has yielded very accurate molecular constants for the X and B states of YCl. Shirley et al. (1990) have studied the molecular-beam optical Stark spectrum of the B n(t = 0)-X (t = 0) band system of YF. The permanent dipole moment and the magnetic hyperfine parameter a for the B n state have been determined as 2.96(4) D and 146.8(3) MHz, respectively. The dipole moment of the X S state was determined as 1.82(8)D. More recently, Shirley et al. (1991) have employed the molecular-beam millimeter-wave optical pump-probe spectroscopy to study pure rotational transitions of the YF ground state. This study has yielded improved ground-state rotational constants as B = 8683.65(1) MHz and D = 0.0079(2)-MHz, respectively. 

For the ease of discussion, we restrict ourselves from now on to the interaction of molecules with a permanent electric dipole moment with electric fields, but the same arguments and principles hold of course for the interaction of particles with a magnetic dipole moment with magnetic fields. In a quadrupole or hexapole focuser, the magnitude of the electric field is zero on the symmetry axis, and this axis is normally made to coincide with the molecular beam axis. Close to this axis, the electric field strength is — to a good approximation — cylindrically symmetric, and it increases with... 

A variety of different methods have been used to measure Vy Vy and Vj (Refs. 1 and 2) only a few of the more important will be discussed here, for asymmetric rotors, both the pure rotational spectrum and its torsion-rotation counterpart are electric dipole allowed and are affected in lowest order by the leading terms in the torsional Hamiltonian. Both types of spectra have been used extensively to determine (Ref 1). For symmetric tops with a single torsional degree of freedom, either the permanent electric dipole moment vanishes, as in CH CHg, or the normal rotational spectrum is independent of in lowest order, as in CHj,SiHj,. In the latter case, the molecular beam avoided crossing method can often be used (Ref 2). The torsion-rotation spectrum is forbidden... 

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