Cross Sections for Rotational Decoherence of Perturbed Nitrogen Measured via Decay of Laser-Induced Alignment

Transient alignment signal for N2 (0.6 atm, 140K). The decay is due to the rotational decoherence caused by inelastic collisions.

Nina Owschimikow, Falk Königsmann, Jochen Maurer, Philipp Giese, Anna Ott, Burkhard Schmidt, and Nikolaus Schwentner

We quantitatively determine cross sections for rotational decoherence from the decay of non-adiabatic laser-induced alignment in nitrogen and nitrogen-foreign gas mixtures in a temperature range between 80 K and room temperature. The cross section for rotational decoherence in pure nitrogen decreases from 102 Ų at 80 K to 48 Ų at 295 K, leading to long-lived coherences even at high temperatures. Comparison with the broadening of the transition lines of the Raman Q-branch reported in the literature shows that the decay of rotational coherence proceeds at the same rate as rotational depopulation. This is verified also for mixtures of nitrogen with hydrogen, helium, argon and krypton. We discuss limits posed by a possible J-dependence of the cross sections and strategies for state resolved determination from the time-dependent alignment signal.

J. Chem. Phys. 133 (4), 044311 (2010)