Transition from molecular complex to quantum solvation in 4HeNOCS

Area of Science:

• Quantum chemistry
• Atomic and molecular physics
• Condensed matter physics

Background:

• The behavior of molecules within helium clusters is crucial for understanding quantum solvation.
• Previous studies have explored small clusters, but a detailed quantum mechanical investigation across variable sizes was needed.

Purpose of the Study:

• To perform fully quantum calculations of rotational energy levels and spectroscopic rotational constants for the linear OCS molecule in helium-4 (⁴He) clusters.
• To investigate the size-dependent evolution of OCS rotational properties as the number of helium atoms increases.

Main Methods:

• Utilized fully quantum mechanical calculations to determine rotational energy levels.
• Computed spectroscopic rotational constants for OCS in ⁴He clusters ranging in size from small complexes to larger droplets.
• Analyzed the transition in molecular behavior based on the calculated rotational constants.

Main Results:

• Rotational constants of OCS decrease initially with increasing helium atoms (up to N=6).
• A minimum in rotational constants is observed, followed by an increase and saturation at larger cluster sizes (N=20).
• This minimum signifies a transition from a near-rigid molecular complex to a quantum-solvated molecule with distinct properties.

Conclusions:

• The observed minimum in rotational constants marks a critical transition in the solvation nature of OCS in helium clusters.
• Quantum solvation is characterized by non-zero permutation exchanges and reduced rigid coupling compared to molecular complexes.
• These findings provide insights into the quantum nature of solvation and molecular behavior in ultracold helium environments.