Rotational transfer

Resonant rotational to rotational (R-R) energy transfer may have rates exceeding the Leimard-Jones collision frequency because of long-range dipole-dipole interactions in some cases. Quasiresonant vibration to rotation transfer (V-R) has recently been discussed in the framework of a simple model [57]. 

McCaffery A J 1999 Quasiresonant vibration-rotation transfer a kinematic interpretation J. Chem. Phys. Ill 7697... 

A somewhat more systematic study has been made of collisional deactivation of vibrationally excited ions. Some diatomic and triatomic systems that have been investigated are included in Table II. Vibrational-to-rotational transfer has been demonstrated95 for vibrationally excited H2+ colliding with helium ... 

These methods provide an accurate means of investigating translation-vibration and translation-rotation transfer. The passage of a sound wave through a gas involves rapidly alternating adiabatic compression and rarefaction. The adiabatic compressibility of a gas is a function of y, the ratio of the specific heats, and the classical expression for the velocity, V, of sound in a perfect gas is... 

Pari design Casting Compression Filament winding Injection Matched die molding Rotational Transfer compression Wet lay-up (contact molding)... 

Optical (Specific) Rotation Transfer about 750 mg of sample, accurately weighed, into a 50-mL volumetric flask, dissolve in and dilute to volume with 20% hydrochloric acid, and mix. Determine the rotation in a 1-dm tube within 15 min. pH of a 1 100 Solution Determine as directed under pH Determination, Appendix IIB. 

Optical (Specific) Rotation Transfer an accurately weighed amount of sample, equivalent to about 100 mg of total tocoph-erols, into a separator, and dissolve it in 50 mL of ether. Add 20 mL of a 10% solution of potassium ferricyanide in a 1 125 sodium hydroxide solution, and shake for 3 min. Wash the ether solution with four 50-mL portions of water, discard the washings, and dry over anhydrous sodium sulfate. Evaporate the dried ether solution on a water bath under reduced pressure or in an atmosphere of nitrogen until about 7 or 8 mL remains, and then complete the evaporation, removing the last traces of ether without the application of heat. Immediately dissolve the residue in 5.0 mL of isooctane, and determine the optical rotation. Calculate the optical rotation [see Optical (Specific) Rotation, Appendix HB], using as c the concentration expressed as the number of grams of total tocopherols, as determined in the Assay (above), in 100 mL of the solution. 

Translation-Rotation Transfer a. Heavy Diatomic Species... 

An additional result of Chen and Moore s study is that a considerable portion, perhaps nearly all, of the vibration-rotation transfer in HC1 is intramolecular The vibrator leaves the collision with the major portion of... 

Using probability theory, the following expression was obtained as the basic rotational transfer function. In practice, this expression is summed over available velocities weighted by their individual probabilities. 

This computational routine for predicting state-to-state probabilities has been shown to give quantitative agreement with experiment for a wide variety of collision-induced processes. These include rotational transfer (RT) [24, 26, 36, 38—40], i.e., state change within a vibrational manifold, vibration-rotation transfer (VRT) [41, 42], i.e., transitions between vibrational states and electronic energy transfer [43], i.e., transitions between discrete levels of different electronic states. An example is given in Fig. 6 in which the calculated data were computed using the... 

Fig. 5 Plot of rotational transfer rate coefficients for state-to-state collision-induced transfer in A(X) Li2 with Ne, Ar and Xe as collision partners from experiment (symbols) and via (5) (full line). Numerous other data sets on a wide range of molecules were found [36] to give fits of similar quality to (5)...

N2. Red, green and blue arrows illustrate the processes of rotational transfer (1), 4000-... 

Fig. 8 Collision-induced rotational transfer in collisions between Ar and N2(0 10) squares), O2(0 12) circles) and OF1(0 3) triangles). Collision conditions are Maxwell-Boltzmann distribution of velocities at 300 K. Note that there is a Aj = 2n selection rule in collision-induced processes for homonuclear diatomic molecules...

The N2-Ar rotational transfer collisions (as with those between 02-Ar ) are relatively little constrained by energy conservation and so reasonably high RT probabilities are expected, and found, in collisions involving these molecules. The situation is very different for VRT, however, where, as Fig. 10 makes clear, all destination channels from Aj = 12 to +16 are energy limited, some very... 

Collision-induced intramolecular vibration-to-rotation energy transfer appears to be inefficient. The evidence for this inference comes from the study of rotational contours in the one collision-induced transition 7 0° in glyoxal. It is found that the emission from 0° has a distribution over rotational transitions that is close to the thermal distribution. But the vibration v-j in glyoxal is a torsional motion, and the axis of torsion very nearly coincides with the smallest axis of inertia of the molecule, so if collision-induced intramolecular vibra-tion-to-rotation transfer were efficient the emission from 0 should have a nonthermal distribution in the quantum number K (which describes quantization of the motion about the smallest axis of inertia). Note, however, that the collision partner used in this experiment was... 

While these observations would be hard to explain in terms of multiphonon relaxation, they are readily understood consequences of the vibration — rotation transfer model. Isotopic substitution will change not only the vibrational frequency of the guest but also the spacing of the rotational levels, and will modify the localized phonon structure. Whereas the vibrational spacing is proportional to the square root of reduced mass, the rotational constant changes even faster, linearly in fi. As a consequence, the closest rotational level to i = 1 is 7= 13 in NH and 7= 16 in ND. Thus, in spite of a smaller vibrational spacing, the deuteride relaxation is a higher order and hence less efficient process. 

The extremely narrowband emission of a laser allows the specific excitation of molecular states. The non-Boltzmann distribution produced by the excitation process is quickly destroyed by radiation processes and collisional deactivation. The relative contribution of these different deactivation channels depends on the nature of the level excited as shown in Fig. 3. In the microwave region where rotational levels are excited, the radiative life time is very long compared to the very efficient rotational relaxation processes (R—R rotation—rotation transfer and R—T rotation—translation transfer). Therefore, the absorbed radiation energy is transformed within a few gas kinetic collisions into translational energy. The situation is similar for... 

The theory of R-R transfer requires complex quantum mechanical calculations, and well-defined selection rules can be obtained. In a sense, the problem is easier than V-V transfer since to a good approximation the vibrational motion of the molecule can be ignored, whereas V-V transfer is almost always accompanied by extensive rotational transfer so that V-R and R-R processes must be considered. 

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