Structure Distribution of Gaseous Ions in Strong Electrostatic Fields

Area of Science:

• Physical Chemistry
• Chemical Physics
• Computational Chemistry

Background:

• Drift tube experiments study ion behavior in gases under electrostatic fields.
• Collision excitation probes energy partitioning and relaxation in molecular degrees of freedom.
• Flexible ions in ion mobility spectrometry show activated vibrational modes and metastable structures.

Purpose of the Study:

• Investigate angular vibrational excitation and relaxation in flexible molecular ions.
• Examine the influence of strong electric fields on molecular ion conformations.
• Understand energy transfer and conformational dynamics in molecular ions.

Main Methods:

• Nonequilibrium molecular dynamics simulations.
• Modeling molecular ions with an intramolecular angular potential.
• Analysis of velocity and angular velocity distribution functions.
• Conformer distribution analysis.

Main Results:

• Unified curves observed for velocity and angular velocity distributions plotted against relative ion-atom collision energy.
• Excitation of angular vibration at high field strengths.
• Continuous interconversion of conformations and attainment of limiting population values.
• Observed orientational alignment with greater perpendicular angular momentum than parallel.

Conclusions:

• Angular vibrational excitation and relaxation are significant for flexible molecular ions at strong fields.
• Conformational dynamics are coupled to vibrational excitation and field strength.
• The observed phenomena are likely general for large flexible molecular ions.