Molecular angular momentum

Figure 1. Cartoon depicting symmetry considerations of the asymptotic wavefunction that influences which potential energy surface is accessed. Representative angular momentum quantum numbers relevant to the process are the total molecular angular momentum exclusive of nuclear spin (f) and the relative orbital angular momentum (/).

Figure 10.6 Two-dimensional REMPI spectrogram of the centrifuged Oj molecules. Ion signal is color coded as a function of the frequency of the ionizing laser field, which undergoes two-photon absorption on the C Yl v = 2) X L v" = 0) transition, and molecular angular momentum, which is defined by...

Following the quenching process further, the system is described best in the body-fixed frame, at least for the smaller internuclear distances. Then no orbital angular momentum can be transferred to the relative internuclear motion lz = 0, and the question arises as to how the electronic orbital angular momentum Lz = 1 of the 3p II) state of Na should be disposed of since the final state has to be 3s 2). The obvious solution is to change the orientation of the molecular angular momentum j, that is, to induce a Aiz= 1 transition in the molecule and thus maintain a constant... 

Pibel, C.D. and Moore, C.B. (1990). Molecular angular momentum reorientation of electronically excited hydrogen (B1E+), J. Chem. 

The experimental inertial moments may also be affected by mechanisms other than the rovib interaction discussed above e.g., by contributions from large-amplitude internal motions or by the coupling of the molecular angular momentum and spin momenta caused by the presence of internal magnetic or electric fields. We shall assume in this review that these generally much smaller effects have been... 

To end this section and the review, we mention briefly the first results from the simulation on laboratory-frame cross-correlation of the type (v(f)J (0)). Here v is the molecular center-of-mass linear velocity and J is the molecular angular momentum in the usual laboratory frame of reference. For chiral molecules the center-of-mass linear velocity v seems to be correlated directly in the laboratory frame with the molecule s own angular momentum J at different points r in the time evolution of the molectilar ensemble. This is true in both the presence and absence of an external electric field. These results illustrate the first direct observation of elements of (v(r)J (0)) in the laboratory frame of reference. The racemic modification of physical and molecular dynamical properties depends, therefore, on the theorem (v(r)J (0)) 0 in both static and moving frames of reference. An external electric field enhances considerably the magnitude of the cross-correlations. 

In Chapter 7 an application of C-13 NMR to study rotational motion of molecules is briefly described. When combined with depolarized light scattering, the magnetic resonance results yield values for the components of the rotational diffusion tensors of some symmetric top molecules. In some circumstances, NMR and ESR methods allow measurement of the relaxation times of the molecular angular momentum (e.g., see McClung and Kivelson, 1968). 

The smallest possible value for the maximum impact parameter clearly is the sum of the van der Waals radii of the collision partners, which we take to be 5.6 A for IJ He, 5.8 A for IJiNe, and 6.4 A for I5 Ar. The corresponding maximum angular momenta, obtained from and the velocities at the upper ends of the effective collision energy ranges foimd experimentally, are 5h, 6h, and I7h, respectively. It seems likely that impact parameters somewhat larger than these are still important for the colhsion process we describe. Using the known rotational constant for I, we conclude that a transfer from orbital to molecular angular momentum... 

The coupling of the molecular angular momentum J with a possible nuclear spin I leads to a precession of J around the total angular momentum F = J 1, which further reduces the molecular orientation [513]. A careful analysis of experiments on optical pumping of molecules gives detailed information on the various coupling mechanisms between the different angular momenta in selected molecular levels [514]. 

Helium gave lower values for the broadening coefficients with smaller differences between the peak as compared to self broadening. This is not surprising as helium is less efficient in the orientation of the molecular angular momentum and less efficient in all the other processes as well. 

Further development of the statistical theory introduced an additional constraint imposed by the conservation of the molecular angular momentum [339] by a more precise specification of the transition complex structure [486] along with the elucidation of the limitations of statistical approximation [179]. 

All of these corrections are close to unity, with S being the most significantly different but even then its effect does not exceed 1.5%. For monatomic species no corrections are of course required, since there is no molecular angular momentum. 

J molecular angular momentum J the rotational quantum number... 

Derivative work, based on this analysis, erroneously assumes degeneracy of the linear combinations when defining a set of orthogonal real orbitals . There is no theoretical basis in the seminal paper to justify this assumption. However, what is clearly implied is that the orbital moment on each carbon atom is directed perpendicular to the molecular plane. The molecular angular momentum is therefore quenched vectorially only for this planar arrangement of the molecule. Torsional distortion which creates residual angular momentum therefore requires work, the true basis of a barrier to rotation. 

Orientation changing collisions can be sensitively detected with polarization spectroscopy (see Sect,10.3). Since the polarized pump wave produces a partial orientation of the molecular angular momentum, which gives rise to a change in polarization of the linearly polarized probe wave, any collisions which change the orientation alter the probe intensity transmitted by the second polarizer in Fig.10.33. Another way to detect these collisions uses saturation spectroscopy, where the angle between the planes of polarization of pump and probe wave are varied and the Lamb dip profile is monitored as a function of 3 [12.6]. 

---