fizyka: Infrared spectroscopy

Evidence: 65 • authority: 72

A molecular vibration is a periodic motion of the atoms of a molecule relative to each other, such that the center of mass of the molecule remains unchanged. The typical vibrational frequencies range from less than 1013 Hz to approximately 1014 Hz, corresponding to wavenumbers of approximately 300 to 3000 cm−1 and wavelengths of approximately 30 to 3 μm. Vibrations of polyatomic molecules are described in terms of normal modes, which are independent of each other, but each normal mode involves simultaneous vibrations of parts of the molecule. In general, a non-linear molecule with N atoms has 3N − 6 normal modes of vibration, but a linear molecule has 3N − 5 modes, because rotation about th…

Evidence: 45 • authority: 92

Near-infrared spectroscopy of micro-solvated protonated methanol.. Gas phase near-infrared (NIR) spectra of micro-solvated protonated methanol, MeOH 2 + ⋯X n (X = Ar, N 2 , and CO; n = 1 and 2), in the region of the first overtones of OH stretches were obtained via infrared photodissociation spectroscopy. Spectral details were analyzed with the support of high-precision ab initio anharmonic simulations. The free OH stretching overtones and combination bands of OH stretch and bend are the main features in this region. The hydrogen-bonded OH stretching overtone transitions exhibit weak and broad characteristics across all solvents (X). This trend increases with the proton affinity of X. Hot b…

Evidence: 45 • authority: 72

Raman spectroscopy (; named after the physicist C. V. Raman) is a spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. Raman spectroscopy is commonly used in chemistry to provide a structural fingerprint by which molecules can be identified. Raman spectroscopy relies upon inelastic scattering of photons, known as Raman scattering. A source of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range is used, although X-rays can also be used. The laser light interacts with molecular vibrations, phonons or other excitations in the system, r…

Evidence: 45 • authority: 72

Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functional groups in solid, liquid, or gaseous forms. It can be used to characterize new materials or identify and verify known and unknown samples. The method or technique of infrared spectroscopy is conducted with an instrument called an infrared spectrometer (or spectrophotometer) which produces an infrared spectrum. An IR spectrum can be visualized in a graph of infrared light absorbance (or transmittance) on the vertical axis vs. frequency, wavenumber or…

Evidence: 35 • authority: 80

Fourier Transform Spectra of Overtone Bands of HCN from 4800 to 9600 cm−1: Some New Transitions of Bending Combination Modes

Evidence: 35 • authority: 80

Fundamental, Binary Combination, and Overtone Modes in Methoxy Adsorbed on Cu(100): Infrared Spectroscopy and Ab Initio Calculations

Evidence: 35 • authority: 88

The Assignment of Overtone and Combination Bands in the near Infrared Spectrum of Polyamide 11. Based on a detailed study of the fundamental vibrations in the mid-infrared (MIR) region and supported by NH/ND-deuteration experiments, variable-temperature and polarisation measurements, the assignment of overtone and combination bands in the near infrared (NIR) spectrum of polyamide 11 (PA11), [–(CH 2 ) 10 –CO–NH–] n , is presented. The results can be readily transferred to the spectral interpretation of homologous aliphatic polyamides thereby providing an improved understanding of the NIR spectra of this class of technically important polymers.

Evidence: 35 • authority: 92

Nonlinear dual-frequency modulation QEPAS using a single laser for resolving overlapping spectral features.. Conventional single-frequency wavelength modulation spectroscopy faces inherent limitations in multi-component gas sensing, due to restricted detection dimensionality and unavoidable trade-offs in modulation parameters. To overcome these issues, we propose a Quartz-Enhanced Photoacoustic Spectroscopy sensing technique based on single-laser dual-frequency superimposed modulation. By simultaneously injecting two independent high-frequency modulation signals, matching the fundamental and overtone resonance modes of a Quartz Tuning Fork(QTF), into a single Distributed Feedback laser, dua…

Evidence: 35 • authority: 92

The Origin of the Frequency-Dependence of OH Stretch Vibrational Lifetimes in Liquid Water.. Polarization-resolved infrared pump-stimulated Raman probe spectroscopy was used to measure the lifetimes of OH stretching vibrations in liquid water, giving rise to polarized and depolarized Raman signals. The lifetime of the OH stretch for the polarized Raman was determined to be 200 fs, in excellent agreement with previous measurements. The lifetime of OH stretches contributing to the depolarized Raman signal was determined here for the first time and was found to be at least two times longer (≥400 fs). With the support of mixed quantum-classical line shape calculations, the experimental lifetime…