Low-Temperature Rotational Relaxation of CO in Self-Collisions and in Collisions with Ne and He

Abstract

The low-temperature rotational relaxation of CO in self-collisions and in collisions with the rare-gas atoms Ne and He has been investigated in supersonic expansions with a combination of resonance-enhanced multiphoton ionization (REMPI) spectroscopy and time-of-flight techniques. For the REMPI detection of CO, a novel 2 + 1' scheme has been employed through the A(1)Pi state of CO. From the measured data, average cross sections for rotational relaxation have been derived as a function of temperature in the range 5-100 K. For CO-Ne and CO-He, the relaxation cross sections grow, respectively, from values of approximately 20 and 7 A(2) at 100 K to values of approximately 65-70 and approximately 20 A(2) in the 5-20 K temperature range. The cross section for the relaxation of CO-CO grows from a value close to 40 A(2) at 100 K to a maximum of 60 A(2) at 20 K and then decreases again to 40 A(2) at 5 K. These results are qualitatively similar to those obtained previously with the same technique for N(2)-N(2), N(2)-Ne, and N(2)-He collisions, although in the low-temperature range (T < 20 K) the CO relaxation cross sections are significantly larger than those for N(2). Some discrepancies have been found between the present relaxation cross sections for CO-CO and CO-He and the values derived from electron-induced fluorescence experiments.

Gyroscopic Effect in Low-Energy Classical Capture of a Rotating Quadrupolar Diatom by an Ion

“…This situation may change when one passes from partners out of a single canonical ensemble to two different canonical ensembles (as is the case in recent work 11,12 ) or rotationally selected partners. Here, it can occur that the intrinsic angular momentum is comparable to the typical capture relative angular momentum especially in the region of low collisions energies, E , B (or translational temperatures, T , T rot ).…”

Rotational Excitations in CO–CO Collisions at Low Temperature: Time-Independent and Multiconfigurational Time-Dependent Hartree Calculations

“…Usually, molecular level populations are not in equilibrium, and the prediction of spectral line intensities depends on the magnitude of collisional excitation rate coefficients with dominant species (H 2 , He, H and also CO). The scattering of CO by various colliders (H, − H 2 , − He, − Ne, − Ar − ) has been intensively studied experimentally and theoretically over the past few decades. Despite the wide range of studies that have been performed on these other CO–X systems, to our knowledge, no rigorous quantum-mechanical calculations have been reported to date on the nonreactive scattering of CO–CO even with simplifications such as the coupled states (CS) or infinite order sudden (IOS) approximations despite the availability of accurate potential energy surfaces (PESs) − for more than a decade.…”

Lineshape analysis of stimulated Raman spectra of the near‐nozzle region of free jet expansions

“…Among them, highresolution spectroscopic techniques, such as visible absorption, [3] diode-laser infrared absorption, [4,5] Fourier transform infrared (FTIR) absorption spectroscopy, [6,7] Fourier transform microwave (FTMW) measurements, [8] resonance enhanced multiphoton ionization (REMPI), [9,10] cavity ring down spectroscopy, [11] or nonlinear Raman spectroscopies (stimulated Raman Spectroscopy (SRS), CARS, etc), [12,13] have been widely used to measure vibrationrotation spectra of molecules cooled in the expansion and for the analysis of phenomena naturally occurring, or externally induced, in free jets and supersonic beams, like nonequilibrium between the molecular degrees of freedom, [9,10] nucleation and clustering of the gas, [11,12] photodissociation and photon-induced reactions, [14,15] or interactions of molecules with fields. [16] In the spectra obtained from jets with techniques that have a great field depth, like infrared absorption, the measured intensity and the profile of the spectral lines are the result of an integration along the line of sight, containing information about the density, temperature, and velocity of the observed particles within the jet.…”