Heterodyned fifth-order 2D-IR spectroscopy of the azide ion in an ionic glass

Abstract

A heterodyned fifth-order infrared pulse sequence has been used to measure a two-dimensional infrared (2D-IR) spectrum of azide in the ionic glass 3KNO3:2Ca(NO3)2. By rephasing a two-quantum coherence, a process not possible with third-order spectroscopy, the 2D-IR spectra are line narrowed, allowing the frequencies, anharmonicities, and their correlations to be measured for the first four (nu=0-3) antisymmetric stretch vibrational levels. In this glass, the vibrational levels are extremely inhomogeneously broadened. Furthermore, the glass shifts the energy of the nu=3 state more than the others, causing an inhomogeneous distribution in the anharmonic constants that are partially correlated to the inhomogeneous distribution of the fundamental frequency. These effects are discussed in light of the strong interactions that exist between the charged solute and solvent. Since this is the first example of a heterodyned fifth-order infrared pulse sequence, possible cascaded contributions to the signal are investigated. No evidence of cascaded signals is found. Compared to third-order spectroscopies, fifth-order pulse sequences provide advanced control over vibrational coherence and population times that promise to extend the capabilities of ultrafast infrared spectroscopy.

Femtosecond stimulated Raman spectroscopy by six-wave mixing

“…For example, the proven negligibility of third-order cascades has motivated simplified three-beam approaches in 3D-IR experiments. 56,57 Cascades are known to significantly challenge offresonant fifth-order Raman spectroscopies conducted on pure liquids and concentrated mixtures. [28][29][30] High sample concentrations are one reason why cascades are so dominant in these systems.…”

“…(11). The direct fifth-order signal field is expressed in terms of these polarization components as 60 where the factor of 1/7 represents the orientational average for all-parallel electric field polarizations, 56 and the wavevector mismatch, ∆k (5) direct , is given for the four and five beam geometries in Tables II and III.…”

Ultrafast 2D–IR Spectroscopy of Transient Species

“…Up to now discussion has been limited to the two-point FFCF as experimental information was available only up to this order. With the advent of T2D-IR spectroscopy and the related technique of 3D-IR spectroscopy proposed recently, [56,57] novel information not only on the coupling of solvation degrees of freedom but on all degrees of freedom that modulate vibrational frequencies can be obtained.…”

Ultrafast 2D IR Vibrational Echo Spectroscopy

“…In this Account we will first introduce the experimental technique and then describe its applications in the study of chemical exchange reactions, 9,18 water dynamics, 19 and chemical analysis. 15 Interesting topics that are not covered here are experiments by Tokmakoff and co-workers on the coupling between vibrational modes, 14 population relaxation, 5 and structure and dynamics of proteins, 10 experiments by Hochstrasser and co-workers on solution dynamics of small molecules, 25 hydrogenbond chemical exchange, 17 and small peptide models of biological systems, 26 experiments by Zanni and co-workers on fifth-order vibrational echo spectroscopy 8 and membrane peptides, 7 and experiments by Fayer and co-workers on hydrogen-bonded oligomers, 6 nanoscopic water, 27 and protein structure and dynamics. 16,28 …”

“…Ultrafast 2D IR vibrational echo spectroscopy [1][2][3][4][5][6][7][8][9][10][11] is an ultrafast IR analog of 2D NMR 12 that directly probes the structural degrees of freedom of molecules. 13 The 2D IR vibrational echo technique involves a three-pulse sequence that induces and then probes the coherent evolution of excitations (vibrations) of a molecular system.…”