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2D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)01:19

2D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)

Heteronuclear single-quantum correlation spectroscopy (HSQC) is a 2D NMR technique that reveals one-bond correlations between hydrogen and a heteronucleus. The HSQC experiment is similar to the heteronuclear correlation experiment (HETCOR) but is more sensitive. In the HSQC spectrum, the proton chemical shift is plotted on the horizontal F2 axis, while the 13C chemical shift is plotted on the vertical F1 axis. The corresponding proton and 13C spectra are also shown. The HSQC contour plot does...
Two-Dimensional (2D) NMR: Overview01:12

Two-Dimensional (2D) NMR: Overview

The 1D NMR spectrum of large and complex molecules like natural products has complicated splitting patterns and overlapping signals, which can be easily interpreted using 2-dimensional (2D) NMR. Unlike 1D NMR, 2D NMR has two frequency axes that provide the coupling information between the nucleus A and nucleus B in a molecule. The process from which 2D spectra are obtained has four steps.
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse.
UV–Vis Spectroscopy: Molecular Electronic Transitions01:16

UV–Vis Spectroscopy: Molecular Electronic Transitions

In Ultraviolet–Visible (UV–Vis) spectroscopy, the absorption of electromagnetic radiation is used to probe the electronic structure of molecules. This technique provides insights into molecular electronic transitions, particularly the movement of electrons between different molecular orbitals. Radiation is absorbed if the energy of the electromagnetic radiation passing through the molecule is precisely equal to the energy difference between the excited and ground states. During this process,...
2D NMR: Homonuclear Correlation Spectroscopy (COSY)01:06

2D NMR: Homonuclear Correlation Spectroscopy (COSY)

Homonuclear correlation spectroscopy, or COSY, is a 2-dimensional NMR technique that provides information about coupled protons. Typically, the geminal and vicinal coupling are observed. For example, consider the COSY spectrum of ethyl acetate, where its 1D proton NMR spectrum is plotted along the vertical and horizontal axes with their corresponding chemical shift scale. Three spots on the diagonal corresponding to the three peaks in the 1D proton spectrum are called diagonal peaks. The COSY...
2D NMR: Overview of Heteronuclear Correlation Techniques01:18

2D NMR: Overview of Heteronuclear Correlation Techniques

Heteronuclear correlation spectroscopy is an analytical technique that investigates the coupling between different types of nuclei, often a proton and an X-nucleus, such as carbon-13 or nitrogen-15. This method is commonly used in nuclear magnetic resonance (NMR) spectroscopy to gain insights into complex chemical compounds' structural and compositional aspects. A typical heteronuclear correlation spectrum displays X-nucleus chemical shifts on one axis and a proton spectrum on the other axis.
2D NMR: Overview of Homonuclear Correlation Techniques01:16

2D NMR: Overview of Homonuclear Correlation Techniques

Homonuclear correlation spectroscopy (COSY) is a powerful technique used in Nuclear Magnetic Resonance (NMR) spectroscopy to study the correlations between nuclei of the same type within a molecule. It provides information about scalar couplings between adjacent nuclei, which helps determine connectivity and structural information. There are several COSY variants, each with its unique strengths and experimental parameters.
COSY90 is the standard two-dimensional (2D) COSY experiment that...

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High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy
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Two-dimensional electronic double-quantum coherence spectroscopy.

Jeongho Kim1, Shaul Mukamel, Gregory D Scholes

  • 1Department of Chemistry, Institute for Optical Sciences and Centre for Quantum Information and Quantum Control, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada.

Accounts of Chemical Research
|June 26, 2009
PubMed
Summary
This summary is machine-generated.

We developed 2D double-quantum coherence spectroscopy (2D-DQCS) to experimentally measure electron correlation in large molecules. This technique quantifies electron-electron interactions, revealing how electron excitations influence molecular electronic structure and chemical properties.

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Area of Science:

  • Physical Chemistry
  • Quantum Chemistry
  • Spectroscopy

Background:

  • Describing the electronic structure of many-electron systems is complex, requiring understanding electron correlation beyond mean-field theory.
  • Accurate chemical descriptions necessitate accounting for electron avoidance, crucial for bonds, reactions, and spectroscopy.
  • Experimental tests for electron correlation in large, condensed-phase molecular systems are needed.

Purpose of the Study:

  • To develop and apply a novel spectroscopic technique for probing electron correlation in excited electronic states.
  • To experimentally measure the energy shifts arising from electron-electron interactions in double-excited states.
  • To investigate the relationship between molecular geometry and electron correlation effects.

Main Methods:

  • Utilized two-dimensional (2D) optical coherent spectroscopy, specifically 2D double-quantum coherence spectroscopy (2D-DQCS).
  • Employed multiple, time-ordered ultrashort coherent optical pulses to generate double- and single-quantum coherences.
  • Analyzed the 2D electronic spectrum to map energy correlations between single- and double-excited states.

Main Results:

  • 2D-DQCS successfully correlated double-excited electronic states with constituent single-excited states.
  • Measured energy offsets for second electronic excitations, revealing electron-electron interaction magnitudes (tens of millielectronvolts).
  • Observed sensitive dependence of these energy offsets on molecular geometry in organic dye molecules.

Conclusions:

  • 2D-DQCS provides quantitative insights into electron-electron interactions and electron correlation in excited states and excitons.
  • The technique elucidates many-electron wave functions and the impact of electron correlation on chemical systems.
  • This work contributes to understanding electronic structure beyond simplified orbital representations.