3 research outputs found
Fully Coherent Triple Sum Frequency Spectroscopy of a Benzene Fermi Resonance
In this paper we present a new multiresonant
coherent multidimensional
spectroscopy (CMDS) technique employing a pathway that is both fully
coherent and necessarily unique. This technique is based on a Triple
Sum Frequency (TSF) coherence pathway with three excitation pulses
having frequencies ω<sub>1</sub>, ω<sub>2</sub>, and ω<sub>3</sub> and the phase matching condition <i>k⃗</i><sub>1</sub> + <i>k⃗</i><sub>2</sub> + <i>k⃗</i><sub>3</sub>. Two-dimensional spectra are created by independently
tuning the ω<sub>1</sub> and ω<sub>2</sub> pulses across
vibrational resonances while monitoring the intensity of a visible
output beam created by a Raman transition induced by the ω<sub>3</sub> pulse. Two-dimensional plots of the coherent dynamics are
created by independently scanning the τ<sub>21</sub> and τ<sub>31</sub> delay times between the different frequency excitation pulses
over all time orderings. TSF CMDS separates fundamental and overtone/combination
band states uniquely onto the ω<sub>1</sub> and ω<sub>2</sub> axes when τ<sub>21</sub> ≠ 0. TSF is valuable
in its ability to probe states of complementary parity to those seen
in Doubly Vibrationally Enhanced Four-Wave Mixing (DOVE-FWM), the
other fully coherent mixed electronic/vibrational CMDS method. This
capability is demonstrated through the use of neat benzene as a model
system, where the center of inversion imposes strict parity selection
rules
Triply Resonant Sum Frequency Spectroscopy: Combining Advantages of Resonance Raman and 2D-IR
This
article describes the new multidimensional spectroscopy technique
triply resonant sum frequency spectroscopy, a four-wave mixing technique
sharing advantages of both 2D-IR and resonance Raman experiments.
In this technique, lasers with three independent frequencies interact
coherently within a sample and generate an output frequency at their
triple summation. The output intensity depends on coupled electronic
and vibrational resonances in the sample. We use an organic dye as
a model system to demonstrate fully resonant, fully coherent multidimensional
spectroscopy using two independently tunable mid-infrared vibrational
interactions and one visible electronic interaction. When the pulses
are time ordered, the method has a single coherence pathway, eliminating
interference between pathways. Fundamental vibrational transitions
appear on one axis and overtones and combinations bands on the other,
allowing anharmonicities of the modes to be determined easily and
conveying molecular coupling information. The experiments demonstrate
coupling between seven vibrational ring modes and an electronic state,
the resolution of a Fermi resonance, detection of low concentrations,
elimination of excitation pulse scattering and fluorescence, background
suppression of solvent and co-solutes, and observation of coherence
dephasing dynamics. The electronic resonance enhancements used in
this methodology are similar to the enhancements responsible for resonance
Raman spectroscopy and can be considered resonance 2D-IR spectroscopy
Resonance IR: A Coherent Multidimensional Analogue of Resonance Raman
This
work demonstrates the use of triply resonant sum frequency
(TRSF) spectroscopy as a “resonance IR” analogue to
resonance Raman spectroscopy. TRSF is a four-wave-mixing process where
three lasers with independent frequencies interact coherently with
a sample to generate an output at their triple summation frequency.
The first two lasers are in the infrared and result in two vibrational
excitations, while the third laser is visible and induces a two-quantum
anti-Stokes resonance Raman transition. The signal intensity grows
when the laser frequencies are all in resonance with coupled vibrational
and electronic states. The method therefore provides electronic enhancement
of IR-active vibrational modes. These modes may be buried beneath
solvent in the IR spectrum and also be Raman-inactive and therefore
inaccessible by other techniques. The method is presented on the centrosymmetric
complex copper phthalocyanine tetrasulfonate. In this study, the two
vibrational frequencies were scanned across ring-breathing modes,
while the visible frequency was left in resonance with the copper
phthalocyanine tetrasulfonate Q band, resulting in a two-dimensional
infrared plot that also reveals coupling between vibrational states.
TRSF has the potential to be a very useful probe of structurally similar
biological motifs such as hemes, as well as synthetic transition-metal
complexes