Direct evidences of scattering resonances enhancement in the vibrational relaxation of by collisions with He at very low temperatures

The vibrational deactivation of I2(B, ν′ = 21) by He in the low energy regime, was studied under single collision conditions, in a supersonic expansion. The time resolved fluorescence signal (TRFS) from the (B; ν′ = 21)→ (X; ν″ = 1) transition was collected at several distances from the nozzle to access different local temperatures in the range (0.17–6) K. From the analysis of the TRFS the value of the relaxation cross-section was extracted and it showed to decrease with energy through a series of peaks. This experimental observation, confirms the role of scattering (mainly orbiting) resonances as theoretically postulated previously.