Transient absorption spectra of vibrationally excited OH/OD groups in mordenite zeolites: Effect of Xe adsorption

Abstract

Transient spectra following the v=1←0 excitation of the OH stretching mode of Bro/nsted acidic hydroxyl groups in normal and deuterated mordenite zeolites have been measured by a two-color picosecond pump–probe technique. When the OH and OD stretching bands were excited by resonant IR pulses, transient bleaching of the fundamental band (v=1←0) and the transient hot band (v=2←1) absorption signal were observed. For the OH and OD groups free of adsorbates, the spectral widths of the pump-induced signals were broadened by ∼4 cm−1 due to pure dephasing from the convoluted width of the pump and probe IR pulses. When the OH and OD groups were adsorbed by a Xe atom, the frequencies of the ν(OH) and ν(OD) bands shifted to lower frequency and at the same time the widths of both the transient bleaching and the transient hot band absorption were much broader than those of the isolated hydroxyl groups by the factor of more than three. Actually, the widths of the transient signals were about the same as those of the linear absorption signals. An adiabatic approximation has been employed to interpret the observed broadening/shift of the IR bands by making use of the results of DFT (density functional theory) calculations performed on a model cluster consisting of a Xe atom and an H3Si–(OH)–AlH3 substrate. The result agreed well with the observed spectral features.

Picosecond infrared pump–probe spectrum of D2O adsorbed at acid OD group of zeolite

“…͑The choice of the Gaussian profile was based on our previous finding for the OH stretching band of the Xe/zeolite system; the spectral feature of the bleach signal was broadened by the fluctuation of hydrogen bond and displayed the Gaussian profile. 6 ͒ It is seen that the extreme position of the deconvoluted bleach signals is shifted by pump frequency while those of the transient absorption band stayed at the same frequency. The population holes that are peaked at the pump frequencies were burned inside the inhomogeneously broadened 3 band and the transient absorption band is dominated by homogeneous width.…”

“…Recent progress in generating intense, turnable, and ultrashort infrared laser pulses has made pump-probe spectroscopy a powerful tool for the investigation of the vibrational dynamics of molecules absorbed on solid surfaces. [1][2][3][4][5][6][7] Specifically, the knowledge of state-to-state vibrational relaxation rate constants enabled us to discuss the coupling between the vibrational mode of the absorbed species and the substrate modes. The observation of the transient spectrum, as induced by the excitation of a specific vibrational mode, enables us to investigate the transient structural change of the absorbed molecule, which is an important aspect of catalytic reactions.…”

Catalytic Aerobic Oxidation of Lignocellulose-Derived Levulinic Acid in Aqueous Solution: A Novel Route to Synthesize Dicarboxylic Acids for Bio-Based Polymers

“…From the FTIR spectra of CA product in Figure 2, an OD peak due to HOOC−COD(CH 3 )− was present at 2680 cm −1 . 46,47 Meanwhile, a methyl group containing D atoms (2230 cm −1 , CD x (H) 3−x ) was observed. 48,49 This is consistent with the results of HPLC-MS (Figure S9) and a 1 H NMR (Figure S10) analysis.…”

Vibrational Relaxation Process of Polyatomic Molecules Adsorbed in Zeolites

“…Species adsorbed in zeolite offers a good model system for the study of vibrational relaxation process on a solid surface [1][2][3][4][5][6][7]. In the present study, the vibrational relaxation lifetimes of the CO stretching mode of Cr(CO)6 and Mo(CO)6 adsorbed on the HY, DY and NaY-type zeolites were measured at various temperature by pump-probe method using picosecond infrared laser pulses.…”