Rotational energy transfer resonances

E.E.Nikitin, J.Troe, and V.G.Ushakov, Classical simulation of the near-resonance rotational energy transfer between two dipole rotors, J.Phys.Chem 98, 3257 (1994)... 

Unlike the case of collision-induced vibrational energy transfer, collision induced rotational energy transfer seems to be free of strong restrictions on the changes in the rotational quantum numbers. When account is taken of the spectral widths of the excitation sources used, the nature of the rotation-vibration structure in the fluorescence and absorption spectra, and the possibility of resonant ener f transfer in the collision, it is concluded that the studies of Bj aniline are the weakest, those of B2 benzene better, and those of glyoxal the best available. With this hierarchy of quality of information kept in mind, the following weaker conclusions can also be obtained from the studies cited. 

Collision-induced rotational relaxation is very much more efficient when resonant transfer of electronic energy is possible than when it is not possible. The cross-sections reported for rotational energy transfer in collisions of Bjy and benzene molecules, and in collisions of... 

To summarize, two important factors controlling the rates of energy transfer involving vibration and rotation are resonance and long-range interactions. The combination of lasers and microwave techniques can be used to study a wide array of vibrational and rotational energy transfer processes. 

Vohralik and Millerl used a crossed molecular beam apparatus to study HF-HF collisions. Laser excitation was used to state select one beam, and the depletion of the excited state gave evidence of resonant rotational energy transfer. Using a kinetic model involving the reasonable assumption that exactly resonant R-R processes dominate the depletion process, they obtained cross sections for one- and two-quantum resonant R-R processes, HF(ji) + HF(j2) - HF(j2) + HF(ji). Their results are given in Table VI. 

Several 3-dimensional studies of the nonreactive quenching of F PipP) in collisions with H2 have been carried out [143-145]. This inelastic scattering process is dominated by near resonant electronic-to-rotational energy transfer,... 

The effects of molecular structure on the rates of energy transfer are manifested in many ways. Additional pathways are available in collisions with molecules, such as the influence of ionic potential surfaces [35], the availability of near resonant electronic-to-vibrational and rotational energy transfer pathways [36], and the introduction of nonadiabatic transitions due to the breaking of the molecular orbital symmetry [37]. For the studies considered here, we might also add the competition between reaction and the desired energy transfer process, the possibility of energy transfer processes in the entrance or exit channels, selective changes in... 

The characteristic energy values for vibrational to vibrational as well as rotational to rotational energy transfer and their weak dependence on temperature relates to the phenomenon of resonance. Transfer becomes less effective when the difference in energies of the modes involved becomes larger. This follows from so-called surprisal analysis (a statistical method) and is due to decreasing cross sections when mode frequencies v become very different. According to surprisal analysis the rate constant for transitions between states labeled v and v depends Boltzmann-like on the energy difference between them ... 

Small-scale laboratory-sized chemical lasers provide convenient sources for studies of the distribution of vibrational energy in chemical reaction products and for measurements of vibrational and rotational energy transfer processes with the laser-induced fluorescence and laser double-resonance techniques. " ... 

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]. 

The intersubunit rotation is required for translocation as ribosomes trapped in the nonrotated state by an engineered intersubunit disulfide bridge fail in tRNA-mRNA movement. Real-time observation of intersubunit movement by fluorescence resonance energy transfer (FRET) showed that intersubunit movement occurs concomitantly with hybrid state formation, and that the rotated state can be trapped by the antibiotic viomycin. Similarly to the fluctuation of tRNAs between classical and hybrid states, single-molecule studies have detected spontaneous intersubunit movement where the 3 OS subunit fluctuates between a rotated... 

Energy near-resonance and favorable overlap of vibrational states are the dominant factors affecting the magnitudes of the charge-transfer cross sections in the AB + -AB systems. It was found188 that an adequate theoretical treatment of the H2+ -H2 system necessitated inclusion of the effects of vibration-rotation interaction in calculating vibrational overlaps from accurate vibrational wave functions. Charge-transfer cross sections were thus computed as a function of different vibrational and rotational levels of the incident-ion species. 

---