Rotational molecular dynamics of laser-manipulated bromotrifluoromethane studied by x-ray absorption

TL;DR

This study uses computational methods to analyze how laser pulses manipulate the rotational dynamics of CF3Br molecules and how resonant x-ray absorption can be used to measure and control this process with high temporal resolution.

Contribution

It introduces a combined computational approach to study laser-controlled molecular rotation and demonstrates the potential of picosecond x-ray pulses for precise measurement of molecular alignment.

Findings

Picosecond x-ray pulses can accurately measure <cos^2 theta>(t) in impulsively aligned molecules.

The transition from impulsive to adiabatic alignment depends on laser intensity and temperature.

Rotational control enables shaping of long x-ray pulses on a picosecond timescale.

Abstract

We present a computational study of the rotational molecular dynamics of bromotrifluoromethane (CF3Br) molecules in gas phase. The rotation is manipulated with an offresonant, 800nm laser. The molecules are treated as rigid rotors. Frequently, we use a computationally efficient linear rotor model for CF3Br which we compare with selected results for full symmetric-rotor computations. The expectation value <cos^2 theta>(t) is discussed. Especially, the transition from impulsive to adiabatic alignment, the temperature dependence of the maximally achievable alignment and its intensity dependence are investigated. In a next step, we examine resonant x-ray absorption as an accurate tool to study laser manipulation of molecular rotation. Specifically, we investigate the impact of the x-ray pulse duration on the signal (particularly its temporal resolution), and study the temperature dependence of the achievable absorption. Most importantly, we demonstrated that using picosecond x-ray pulses, one can accurately measure the expectation value <cos^2 theta>(t) for impulsively aligned CF3Br molecules. We point out that a control of the rotational dynamics opens up a novel way to imprint shapes onto long x-ray pulses on a picosecond time scale. For our computations, we determine the dynamic polarizability tensor of CF3Br using ab initio molecular linear-response theory in conjunction with wave function models of increasing sophistication: coupled-cluster singles (CCS), second-order approximate coupled-cluster singles and doubles (CC2), and coupled-cluster singles and doubles (CCSD).