Role of pure dephasing in the decay of K2 vibrational coherence on helium nanodroplets

Determine whether the gradual decay of the oscillation amplitude in the time-dependent expectation value of the internuclear separation, ⟨R⟩(t), observed for K2 in the 1^3 state on the surface of helium nanodroplets is caused solely by vibrational relaxation due to dissipation of vibrational energy into the droplet, or whether pure dephasing also contributes to the decay.

Background

The paper measures long-lived oscillations in the mean internuclear separation ⟨R⟩(t) of K2 (1^3 state) on helium nanodroplets using time-resolved Coulomb explosion imaging, and extracts a decay constant of approximately 260 ps for the oscillation amplitude.

By analogy with previous work on Rb2, the authors attribute the decay primarily to vibrational relaxation via coupling to the helium droplet environment, but explicitly note that an additional contribution from pure dephasing cannot be excluded with the present data and analysis.