A new method of measuring the hydrogen bond stretching frequency νσ of a complex in solution

Pump-probe spectroscopy of H-bonds as the level-crossing problem

“…In contrast, an X-H intramolecular transition is essentially quantum and only the lowest two states of this oscillator, vϭ0 and 1, are really in resonance with the monochromatic pumping light at high anharmonicity. The frequency of this transition ⍀ϭ͓U 1 (q)ϪU 0 (q)͔/ប is often assumed to be linear in q: [1][2][3][4] ⍀ϭ⍀ 0 ϩFq, ͑1.1͒…”

Vibrational Dephasing Mechanisms in Hydrogen-Bonded Systems

“…Recent developments in timeresolved spectroscopy have allowed for, e.g., the measurement of homogeneous vibrational line shapes with IR transient hole-burning techniques [2,3] and the timeresolved observation of vibrational dephasing by means of a photon-echo experiment [4]. A great number of sophisticated models have been developed to describe vibrational line shapes [5][6][7][8][9][10], some specifically addressing the effect of hydrogen bonds [8][9][10]. The spectral bandwidth of a hydrogen-bonded complex is typically an order of magnitude larger than that of the unassociated molecule or oscillator, indicating that the vibrational dephasing rate is strongly influenced by hydrogen-bond formation.…”

“…Conversely, Robertson and Yarwood predict a narrowing of the line, since in their model the coordinate r s determines the dephasing directly and r s ͑t͒ will fluctuate more rapidly with increasing n s ͑XH · · · Y) frequency. If the stochastic modulation of r s is described by an OrnsteinUhlenbeck process [10], then the rate of frequency modulation of the n s (X-H) mode is determined by the frequency of the hydrogen-bond stretching mode n s , as well as a damping parameter g: t c g͞n 2 s . The frequency of the n s mode can be modified simply by changing the adsorbate.…”

“…The key point of these theories was the recognition that dephasing of the n s (X-H) stretch vibration occurs through coupling to the hydrogen bridge stretching mode n s (XH· · · Y), directed along the same spatial coordinate as the n s (X-H) highfrequency mode itself; the coordinate of the n s ͑XH · · · Y) mode r s determines the frequency of the n s (X-H) mode. In the extension of this model by Robertson and Yarwood [10] the dynamics of the coupling were incorporated by introducing a stochastic modulation of the r s coordinate superimposed on the n s ͑XH · · · Y) vibration. This causes a frequency modulation of the high-frequency n s (X-H) mode through the time evolution of r s .…”

Pump-probe spectroscopy of H-bonds: Saturation kinetics and spectral transformation during and after pumping

“…Usually, the time-dependent modulation is considered as a Gaussian random process. [2][3][4][5][6][7][8][9][10][11] However, in the case of saturation spectroscopy, nonlinear interaction of the vibrational transition with a strong laser field disturbs the stochastic motion and leads to non-Gaussian statistics.…”