Victor M. Blunt

Piezoelectric detection of vibrational overtones at cryogenic temperatures

A resonant optoacoustic technique is described using continuous wave laser excitation and piezoelectric detection of overtone absorptions of liquefied gases at cryogenic temperatures. This technique uses a piezoelectric detector directly attached to a low temperature cell inside a cryostat. The liquefied sample inside the cell is vibrationally excited in the visible region with a continuous wave dye laser. The laser is modulated around 100 kHz with an acousto‐optic modulator. The modulation frequency corresponds to an acoustic resonance frequency of the cylindrical cell which increases the sensitivity of the detection system. The pressure wave detected by the piezoelectric transducer is sent to a lock‐in amplifier and processed with a microcomputer. This sensitive technique is used to obtain the visible spectra of pure liquid methane and ethane. Spectra of the fourth overtone of the C‐H stretch vibration of methane, in solution with liquid argon at 94 K, and in solution with liquid nitrogen at 84 K, are a...

Vibrational spectroscopy of CH bonds of methane and tetramethylsilane in liquid argon solutions

Abstract The liquid phase spectra of the fundamental and first overtone (Δ v = 1, 2) around the CH stretch of methane and tetramethylsilane in liquid argon solutions have been measured using Fourier transform IR and near-IR techniques. The fourth overtone (Δ v = 5) of the CH stretch has been measured in methane pure at 116 K and in liquid argon solutions at 100 K using laser excitation with acoustic detection. The results indicate that absorption bands, which normally present extensive inhomogeneous congestion, could be simplified by studying the absorptions in diluted solutions at low temperatures with inert liquefied gases as solvents.

Vibrational ab initio calculations and spectra of C–H bonds of trimethylboron

Visible laser photoacoustic and near‐IR spectra of the overtones of the C–H stretches of (CH3)3B in the gas phase are reported. Two bands are assigned to nonequivalent methyl C–H bonds. The interaction of an empty 2p orbital of the boron atom with the C–H bonds of a methyl group changes the strength of the C–H bonds during the internal rotation. The most intense, higher energy absorption band in each overtone region is assigned to the CH bonds in the molecular plane (C–H∥) and the least intense, lower energy absorption band to the CH bonds out of the molecular plane (C–H⊥). To interpret the experimental results, overtone transitions are described in terms of the local mode model. A harmonically coupled anharmonic oscillator (HCAO) model was used to determine the overtone energy levels and assign the absorption bands to particular transitions. Ab initio molecular orbital calculations were also performed. Equilibrium geometries, vibrational frequencies, and infrared intensities were calculated at the Hartre...

Vibrational overtone spectroscopy of CH2D2 in liquid argon solutions

Abstract The spectra of the fundamental and overtones of the CH ( ν = 1–5) and CD ( Δν = 1, 2, 3) stretches of CH 2 D 2 have been measured in liquid argon solutions at temperatures between 94 and 101 K. Absorption in the visible was obtained with a low temperature cell and a resonant continuous wave laser technique with acoustic detection. Absorptions in the IR and near-IR were observed with a Fourier transform spectrophotometer. To interpret the experimental results, overtone transitions are described in terms of the local mode model. The harmonically coupled anharmonic oscillator (HCAO) model was used to determine the overtone energy levels and assign the absorption bands to vibrational transitions. The linewidths of the fundamental and overtone transitions are discussed in terms of rotational relaxation for the fundamental bands and vibrational relaxation in the form of dephasing for the overtones.

Vibrational spectroscopy of nonequivalent CH bonds in liquid cis- and trans-3-hexene

Abstract The liquid phase vibrational fundamental and overtone spectra (Δν = 1–4) of nonequivalent CH bonds of cis -3-hexene and trans -3-hexene have been recorded using FTIR and near-IR spectroscopy. A technique which uses a piezoelectric detector, lock-in amplification, and a continuous wave dye laser modulated at 80 kHz with an acousto-optic modulator, has been used to detect the fourth (Δν = 5) and fifth (Δν = 6) overtones. The overtone bands have been computer deconvoluted to obtain information with respect to peak position and bandwidth of the overtone absorptions. Transitions corresponding to different CH bonds, olefinic (CH), primary (CH 3 ) and secondary (CH 2 ) are assigned using the local mode model. Other bands are assigned as local mode—normal mode combination bands. Local mode frequencies ω i and anharmonicities X ii are obtained for all the nonequivalent CH bonds. The results obtained for cis -3-hexene are used to interpret the Δν = 3 and 4 CH overtone spectra of cis -1,4-polybutadiene.