Ultrafast Vibrational Energy Transfer in the Layers of D2O and CO on Pt(111) Studied with Time-Resolved Sum-Frequency-Generation Spectroscopy
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- 作者：Masashi Nagao ; Kazuya Watanabe ; Yoshiyasu Matsumoto
- 刊名：Journal of Physical Chemistry C
- 出版年：2009
- 出版时间：July 9, 2009
- 年：2009
- 卷：113
- 期：27
- 页码：11712-11719
- 全文大小：339K
- 年卷期：v.113,no.27(July 9, 2009)
- ISSN：1932-7455
文摘
Ultrafast dynamics of vibrational energy transfer in overlayers of D2O and CO on Pt(111) have been investigated by femtosecond time-resolved (TR) IR−visible sum-frequency-generation (SFG) spectroscopy under ultrahigh-vacuum conditions. About 10 layers of D2O ice were epitaxially grown on c(4 × 2)-CO/Pt(111). The surface was excited by subpicosecond laser pulses, and subsequent energy transfer through low-frequency modes of adsorbates was monitored in terms of peak shifts and broadenings of C−O and O−D stretching bands in SFG spectra as a function of the pump−probe delay. Because D2O ice forms islands, there are two types of CO: one interacting with D2O and the other free from D2O. Simulations of the TR-SFG spectra by using a phenomenological model for the energy-transfer dynamics indicate that the coupling rate of perturbed CO is larger than that of free CO by a factor of 1.7; this is probably because CO 2π* states shift toward the Fermi level due to interaction with D2O. Two isolated bands at 2668 and 2713 cm−1 were assignable to the OD stretching bands of D2O directly interacting with CO at the D2O/CO interface and D2O at the vacuum/ice interface, respectively. Analysis of the temporal spectral changes of free D2O by using a diffusive thermal transport model indicates that heat transfer through low-frequency phonons of the ice layers occurs within 3 ps; this is substantially faster than the pulsed laser-induced melting of thin ice films reported previously.