Linear spectrum of 1 M solution in D2O (black line). The asymmetric stretch vibration is found at 2044 cm−1 and the OD-stretch band is a wide, asymmetric peak with a maximum at ∼2510 cm−1 (blue dashed line). The OD-stretch band of pure D2O (green line) is shown for comparison.
Two-color 2D-IR spectra of in D2O at population times t2 = 300, 400, and 1200 fs. Initially, a rather narrow and weak bleach/stimulated emission signal is observed (blue band), whose frequency coincides with the maximum of the linear absorption spectrum (blue dashed line, as in Fig. 1). Furthermore, a much broader excited state absorption signals is observed (red band). The bleach contribution grows in time, while the excited state absorption peak decays. After ∼1 ps, thermalization dominates in the form of a strong and wide bleach contribution.
Cuts of 2D-IR spectra at t2 = 400 fs along ω pump = 2048 cm−1 comparing 2D-IR signal sizes for in D2O with in H2O. Since no 2D-IR response in H2O is observed, the measured signal in D2O originates from an intermolecular cross-peak.
Time dependence of the intensity of the peak of the 1–2 excited state absorption signal. The data are fit by Eq. (4), revealing the two time constants τ1 = 150 fs and τ2=1.7 ps.
Vibrational level scheme for coupled oscillators and the possible origins of 2D-IR cross-peaks. The symmetric stretch of and OD-stretch are coupled and share a common ground state. The pump pulse induces a transition into the first excited state of the asymmetric stretch vibration of . In the direct coupling case, the probe pulse moves the excitation up to the |11⟩ state. In the case of population transfer, the oscillation moves from the |10⟩ to the |01⟩ state and the probe pulse induces further absorption into the |02⟩ state.
Linear spectra of saturated KSeCN (black line) and KSe13CN (red line) solutions in D2O. CN-stretches are observed at 2070 and 2020 cm−1 for KSeCN and KSe13CN, respectively. The OD-stretch band is split into two peaks, with the shape and intensities being almost identical for both salts. In a KSeCN and KSe13CN solution in H2O, two combination bands of the ion are visible – one between the CN-stretch and the SeCN bend and the other between the CN- and SeC-stretches (green line for KSeCN, blue line for KSe13CN, both upscaled by ∼×50).
KSeCN and KSe13CN in D2O. (a) Linear spectra of the OD-stretch in KSeCN solutions in D2O and the combination bands of KSeCN (green line) and KSe13CN (blue line) (b) 2D-IR spectrum of KSe13CN in D2O at population time t 2=400 fs, (c) 2D-IR spectrum of KSeCN in D2O at t 2 = 400 fs. Upon 13C labeling, the 2D-IR cross-peaks shift not only in the pump frequency, ω pump , but also in the probe frequency, ω probe .
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