Collisional decoherence and rotational quasirevivals in asymmetric-top molecules

Abstract

We demonstrate the observation of quasi-periodic revivals out to 27 ps in an impulsively-aligned asymmetric-top molecule, sulfur dioxide (SO 2), at high sample temperature and density (295 K, 0.5 bar). We find that the asymmetric top exhibits a strong correlation between population alignment and population lifetime (r = 0.97), in accordance with the trend observed in linear molecules. We use a linear birefringence measurement fit to a full quantum simulation of the asymmetric rotor, and are able to separately measure both the population (T 1) and coherence (T 2) lifetimes of the rotational wavepacket. Additionally, we observe a high rate of elastic decoherence (T * 2 = 9.6 ps), and attribute this to long-range interactions mediated by the permanent dipole of the SO 2 molecule. We propose the use of birefringence measurements to study intermolecular interactions in a coherent ensemble, as a step toward using field-free alignment to investigate reaction dynamics and dissipative processes.

Theoretical study of asymmetric super-rotors: Alignment and orientation

“…They are more marked for the rotational groundstate as initial state, where the maximum peaks for cos 2 θ Zz and cos 2 θ Xy are 0.459 and 0.516 and are located at t ≈ 144.5 ps. The alignment factors are mainly driven by C-type revivals [53,54], being the revival time T rev = 57 ps, in accordance to the experimental measurements [35] and the rotational dynamics described in Sec. III A.…”

Rotational Control of Asymmetric Molecules: Dipole- versus Polarizability-Driven Rotational Dynamics

“…In this case the dipole interaction term averages out after few oscillations of the fields, and the rotational dynamics is induced via the anisotropic polarizability components of the molecule ( Fig.1). As was previously shown [11,12,15,10,9], the interaction with a linearly polarized optical field is given by much slower than the optical field, the molecular dipoles are able to follow the field throughout the excitation, namely the interaction is of resonant nature [29,34].…”

“…We present both the terahertz-and optical-induced dynamics of SO 2 serving as an asymmetric top molecular model and has been the subject of recent works in the field [10,11,33].…”

“…Simulating the rotational dynamics of asymmetric top molecules is far more computationally demanding than linear or symmetric top molecules owing to the existence of three-coupled rotational degrees of freedom associated with the three different principal moments of inertia [8,9,10,11]. At ambient temperatures the large number of thermally occupied states makes exact calculation methods very costly in terms of computation time, and in many cases practically not feasible.…”

Ultrafast collisional dissipation of symmetric-top molecules probed by rotational alignment echoes

“…Indeed, most real gas media being at non-negligible pressure, intermolecular collisions affect the spectral properties of radiative processes as well as the energy redistribution over the internal and external degrees of freedom of the system. In the past few years [5][6][7][8][9][10], quantum rotational revivals of molecular alignment induced by a single laser pulse have been successfully used to investigate the collisional relaxation in low-pressure gases.…”