Molecular Structure and Chirality Detection by Fourier Transform Microwave Spectroscopy

Abstract

We describe a three-wave mixing experiment using time-separated microwave pulses to detect the enantiomer-specific emission signal of the chiral molecule using Fourier transform microwave (FTMW) spectroscopy. A chirped-pulse FTMW spectrometer operating in the 2-8 GHz frequency range is used to determine the heavy-atom substitution structure of solketal (2,2-dimethyl-1,3-dioxolan-4-yl-methanol) through analysis of the singly substituted (13)C and (18)O isotopologue rotational spectra in natural abundance. A second set of microwave horn antennas is added to the instrument design to permit three-wave mixing experiments where an enantiomer-specific phase of the signal is observed. Using samples of R-, S-, and racemic solketal, the properties of the three-wave mixing experiment are presented, including the measurement of the corresponding nutation curves to demonstrate the optimal pulse sequence.

Structure Determination, Conformational Flexibility, Internal Dynamics, and Chiral Analysis of Pulegone and Its Complex with Water

“…It has been worked out before that an optimal M3WM signal is obtained for drive pulse durations fulfilling π/2 Rabi conditions, thus inducing maximum coherence between the two states involved. The twist pulse durations should fulfill π pulse conditions . The π twist pulse transfers coherence from the 5 24 ←5 14 (induced by the π/2 drive pulse) to the 5 14 ←5 23 , which is then recorded (Figure , cycle 1).…”

“…The twist pulse durations should fulfill p pulse conditions. [47] The p twist pulse transfers coherence from the 5 24 ! 5 14 (induced by the p/2 drive pulse) to the 5 14 !…”

Two-Path Interference for Enantiomer-Selective State Transfer of Chiral Molecules

“…Then fast schemes of nonadiabatic dynamic were proposed using resonant ultrashort pulses [38][39][40]. Lately, a lot of remarkable experiments were contributed to the verification of enantiomeric differentiation and the probe of enantiomeric excess based on the technique of microwave three-wave mixing (M3WM) [41][42][43][44][45][46][47][48]. Promoted by experimental achivements, some proposals were put forward very recently for the related issues, such as the design of cyclic three-level configurations in chiral molecules [49], shortcut-to-adiabatic (STA) enantiomerselective population transfer of chiral molecules by means of shaped pulses [50,51], and dynamic methods for the enantiomeric excess determination [40] and the innerstate enantio-separation [52].…”

Robust and highly efficient discrimination of chiral molecules through three-mode parallel paths

“…Owing to the property of broken symmetry, one-photon and two-photon processes can coexist in a three-state configuration of chiral molecules, based on which physical (especially optical) methods [9] have been becoming a promising alternative instead of chemical techniques, providing time-saving, convenient, and economical enantiomer-separation. Methods based on a closed-loop three-state (∆-type) system with microwavedriven rotational transitions is important and interesting [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. All above theoretical [10][11][12][13][14][15] and experimental [16][17][18][19][20][21][22][23][24][25] schemes base on the fact that the combined quantity defined by the triple product of three dipolemoment components is of opposite sign between enantiomers.…”