Intensities in local mode overtone spectra of dimethyl ether and acetone

Abstract

Gas phase overtone spectra of dimethyl ether (6.V CH = 2-5) and acetone (6.V CH = 3) are measured using conventional near infrared (NIR) spectroscopy. Intracavity dye laser photoacoustic spectroscopy (lDL-PAS) has been used to measure the 6.v CH = 5-7 gas phase spectra of both dimethyl ether and acetone. Oscillator strengths are calculated using a harmonically coupled anharmonic oscillator local mode description to obtain the vibrational wave functions and ab initio molecular orbital (MO) calculations to obtain the dipole moment function. The calculations, which use no adjustable parameters, can account for the magnitude of the intensities and for the falloff in intensity with increasing v, for both molecules. It can also account reasonably well for the relative intensity of various peaks within a given vibrational manifold and for the relative intensity in the spectra of these two molecules and of propane. Rop = 1.0863 A, R,p = 1.0811 A,LH"pCH"p = 107.21°, and LH,pCH"p = 109.54° for acetone.

Trace species detection in the near infrared using Fourier transform broadband cavity enhanced absorption spectroscopy: initial studies on potential breath analytes

“…As a consequence of its structural similarity with butadiene, isoprene exhibits a very similar spectral fingerprint to butadiene, especially at the low resolution (16 cm -1 ) in figure 2(A). The overtone and combination spectrum of acetone in this region results from excitation of the in-plane (ν 3 ) and out-of-plane (ν 1 , ν 2 ) CH oscillators described by the notation |ν 1 ν 2  +/-|ν 3  according to Kjaergaard et al [27]. A single sharper feature is observed in the spectrum of acetone (near 1672 nm), apparent at higher resolution, which is coincident with the |10 +/-|1 modes as described in [27].…”

Near-IR photodissociation of peroxy acetyl nitrate

“…1) closely resemble the spectra of acetone and acetaldehyde (Hanazaki et al, 1985). The orientational site splitting pattern arising from the inequivalence of CH bonds in the methyl group (Hanazaki et al, 1985;Kjaergaard et al, 1991) is similar for all three molecules. The integrated intensities (per methyl group) for the ν CH fundamental, 2ν CH first overtone, and 3ν CH second overtone bands are also quite similar ( Table 1).…”

“…To evaluate the efficiency of near-IR photochemistry of PAN, knowledge of both the intensity of the CH stretching overtones and photodisssociation quantum yields are required. Although the strength of CH stretching overtone transitions are well-known for many hydrocarbons (Hanazaki et al, 1985;Kjaergaard et al, 1991;Nakagaki and Hanazaki, 1986), no information on the cross sections and photodissociation quantum yields for PAN is presently available. In what follows, we show that these quantities can be estimated from statistical models and comparisons with experimental data on related molecules, and we use them to predict the near-IR photodissociation rates for PAN under typical atmospheric conditions.…”

MIR and NIR group spectra of n-alkanes and 1-chloroalkanes

“…In contrast, the location of both symmetric and asymmetric CH 2 stretching bands strongly depends on the neighboring groups. Numerous works demonstrated that the overtones region is also sensitive on the chain conformation [9][10][11][12][13][14]. The better peaks separation in the NIR spectra made possible to resolve the absorption from the axial and equatorial CH bonds in NIR spectrum of cyclohexane [13].…”

“…As a result, the corresponding spectra are complex due to possibility of various resonances. In contrast, the higher overtones spectra are simple due to the local character of the vibrations [9][10][11][12][13][14].…”