Accurate Line Shapes from Sub-1 cm^–1 Resolution Sum Frequency Generation Vibrational Spectroscopy of α-Pinene at Room Temperature

Abstract

Despite the importance of terpenes in biology, the environment, and catalysis, their vibrational spectra remain unassigned. Here, we present subwavenumber high-resolution broad-band sum frequency generation (HR-BB-SFG) spectra of the common terpene (+)-α-pinene that reveal 10 peaks in the C-H stretching region at room temperature. The high spectral resolution resulted in spectra with more and better resolved spectral features than those of the Fourier transform infrared, femtosecond stimulated Raman spectra in the bulk condensed phase and those of the conventional BB-SFG and scanning SFG spectroscopy of the same molecule on a surface. Experiment and simulation show the spectral line shapes with HR-BB-SFG to be accurate. Homogeneous vibrational decoherence lifetimes of up to 1.7 ps are assigned to specific oscillators and compare favorably to lifetimes computed from density functional tight binding molecular dynamics calculations. Phase-resolved spectra provided their orientational information. We propose the new spectroscopy as an attractive alternative to time domain vibrational spectroscopy or heterodyne detection schemes for studying vibrational energy relaxation and vibrational coherences in molecules at molecular surfaces or interfaces.

Structural Characterization of Single-Stranded DNA Monolayers Using Two-Dimensional Sum Frequency Generation Spectroscopy

“…The peak pairs can be 180° out-of-phase with the 2D IR peaks, the intensities can be very different or nonexistent, and cross peaks between two coupled modes do not have to appear both above and below the diagonal. These differences have been described previously in the context of symmetry selection rules 53 , 72 . We summarize this previous discussion and generalize to vibrational modes with different transition dipoles and hyperpolarizability, which has not been described previously.…”

“…Optimizing a geometry by matching the intensities and phases of the diagonal peaks is similar to methods for matching 1D SFG spectroscopy 72 . Polarization might also be used, but it does not work well on gold surfaces 71 , 73 .…”

Probing the early stages of solvation of cis-pinate dianions by water, acetonitrile, and methanol: a photoelectron spectroscopy and theoretical study

“…Photoelectrons were collected at nearly 100% efficiency by the magnetic-bottle and analyzed in a 5.2 m long electron flight tube. The TOF photoelectron spectra were converted into electron kinetic energy spectra by calibration with the known NIPE spectra of I − and OsCl 6 2− . The electron binding energies (EBEs), given in the spectra in Figs.…”

Sum frequency generation vibrational spectroscopy (SFG-VS) for complex molecular surfaces and interfaces: Spectral lineshape measurement and analysis plus some controversial issues

“…Even though the nanosecond scanning SFG-VS can achieve sub-wavenumber spectral resolution [74], but to obtain a spectral with such resolution by scanning is time-consuming, and the spectra quality is subject to the laser energy fluctuations and the stability of the laser pulse properties over time [65]. The recently developed sub-wavenumber high-resolution broadband SFG-VS (HR-BB-SFG-VS) with resolution as high as ~0.6 cm -1 has shown to be an effective alternative to achieve high enough spectral resolution and obtain accurate lineshape for spectral analysis, and it has revealed many unprecedented details of the molecular structure and interactions of molecular surfaces and interfaces [13,31,66,[75][76][77][78][79]. Particularly, spectral lineshape analysis in SFG-VS in the frequency domain has usually been neglected since the lower resolution measurement usually does not provide accurate enough data to allow such analysis.…”