Related Experiment Video
Updated: Feb 22, 2026
08:22
Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization
Published on: August 6, 2018
7.4K
Vibrational Feshbach Resonances Mediated by Nondipole Positron-Molecule Interactions
M R Natisin1, J R Danielson1, G F Gribakin2
1Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
Physical Review Letters
|September 27, 2017
Summary
New measurements reveal positron-molecule interactions beyond dipole coupling. Positron binding and resonances are observed with infrared-inactive modes, suggesting new theoretical pathways for understanding these exotic states.
Area of Science:
- Atomic and Molecular Physics
- Quantum Chemistry
- Chemical Physics
Background:
- Positron-molecule annihilation studies reveal positron binding and vibrational Feshbach resonances.
- Current theories successfully explain resonances involving infrared-active vibrational modes via dipole coupling.
- Understanding these interactions is crucial for advancing quantum chemistry and materials science.
Purpose of the Study:
- To investigate positron-molecule annihilation resonances associated with infrared-inactive vibrational modes.
- To explore the role of nondipole interactions in forming positron-molecule bound states.
- To identify theoretical requirements for describing these newly observed interactions.
Main Methods:
- Utilized a novel cryogenic positron beam with enhanced energy resolution for precise measurements.
- Conducted energy-resolved measurements of positron-molecule annihilation.
- Analyzed resonance structures in annihilation cross-sections.
Main Results:
- Observed evidence of resonances linked to infrared-inactive vibrational modes in positron-molecule systems.
- Demonstrated that nondipole interactions can populate positron-molecule bound states.
- Provided experimental data challenging existing theoretical frameworks limited to dipole coupling.
Conclusions:
- Positron-molecule bound states can be formed through nondipole interactions, expanding beyond dipole coupling mechanisms.
- The findings necessitate the development of new theoretical models to fully describe these interactions.
- This research opens new avenues for studying exotic quantum states in matter.
Related Concept Videos
01:14Molecular Spectroscopy: Absorption and Emission
4.8K
Molecules possess discrete energy levels called quantum states. Unlike atoms, which have simpler energy levels, molecules possess additional rotational and vibrational energy levels. Each energy level is separated by an energy gap, with the gaps between adjacent electronic, vibrational, and rotational levels varying significantly. The three types of energy levels in a diatomic molecule are shown in Figure 1.
4.8K
01:08Spin–Spin Coupling Constant: Overview
1.5K
In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
1.5K
01:20¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)
1.8K
When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
1.8K
01:12Double Resonance Techniques: Overview
797
Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
Spin decoupling is usually achieved by...
797
01:24IR Spectroscopy: Molecular Vibration Overview
4.9K
When Infrared (IR) radiation passes through a covalently bonded molecule, the bonds transition from lower to higher vibrational levels. The fundamental vibrational motions that result in infrared absorption can be classified as stretching or bending vibrations.
Stretching vibrations are vibrational motions that occur along the bond line, changing the bond length or distance between two bonded atoms. They are further distinguished as symmetric or asymmetric. In symmetric stretching, the...
Stretching vibrations are vibrational motions that occur along the bond line, changing the bond length or distance between two bonded atoms. They are further distinguished as symmetric or asymmetric. In symmetric stretching, the...
4.9K
01:13¹H NMR: Complex Splitting
2.0K
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
2.0K