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Thermal decomposition of CH3CHO studied by matrix infrared spectroscopy and photoionization mass spectroscopy
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10.1063/1.4759050
/content/aip/journal/jcp/137/16/10.1063/1.4759050
http://aip.metastore.ingenta.com/content/aip/journal/jcp/137/16/10.1063/1.4759050

Figures

Image of Scheme 1.
Scheme 1.
Image of Scheme 2.
Scheme 2.
Image of Scheme 3.
Scheme 3.
Image of FIG. 1.
FIG. 1.

A schematic view of the pulsed μtubular reactor used for thermal decomposition of organic substrates. Samples are photoionized with fixed frequency VUV light and the ions are detected by a time-of-flight mass spectrometer.

Image of FIG. 2.
FIG. 2.

A schematic view of the pulsed μtubular reactor used for thermal decomposition of organic substrates. Samples are collected in a 20 K cryogenic matrix for analysis by infrared absorption spectroscopy.

Image of FIG. 3.
FIG. 3.

Photoionization mass spectra of the thermal cracking products of acetaldehyde are shown. The fixed-frequency PIMS uses the 9th harmonic of a YAG laser, 118.2 nm or 10.487 eV, for photoionization. Typical samples have 0.3% acetaldehyde mixed with 2 atm He and heated in pulsed reactor. There are 4 different spectra in this figure. Bottom trace: CH3CHO traversing the μtubular reactor at room temperature; 2nd trace is CH3CHO heated to 1000 K by the μtubular reactor: 3rd trace is CH3CHO heated to 1400 K in the μtubular reactor, 4th trace (red) is CH3CHO traversing the μtubular reactor heated to 1600 K.

Image of FIG. 4.
FIG. 4.

The photoionization efficiency (PIE) curves from the LBNL's Advanced Light Source that result from heating CH3CHO in a CW reactor. The three spectra in the right hand panel show the appearance of m/z 44 when samples of CH3CHO (1% acetaldehyde in He) are passed through the SiC tube at 300 K, 800 K, and 1200 K. The ionization energy of acetaldehyde is known49 to be 10.2295 ± 0.0007 eV. The panel on the left shows the appearance of m/z 43 when CH3CHO is heated by the μtubular reactor to 300 K, 800 K, and 1200 K.

Image of FIG. 5.
FIG. 5.

Photoionization mass spectra of the thermal cracking products of acetaldehyde-d1 are shown (0.5% CH3CDO in He). The fixed-frequency PIMS uses the 9th harmonic of a YAG laser, 118.2 nm or 10.487 eV, for photoionization. There are 4 different spectra in this figure. Bottom trace: CH3CDO traversing the pulsed μtubular reactor at 300 K; 2nd trace is CH3CDO heated to 1300 K by the μtubular reactor; 3rd trace (red) is CH3CDO heated to 1400 K by the μtubular reactor, 4th trace is CH3CDO traversing the μtubular reactor heated to 1500 K.

Image of FIG. 6.
FIG. 6.

An expanded spectrum of the mass range 14–20 amu for the 118.2 nm VUV photoionization of acetaldehyde-d1 heated in a pulsed reactor is shown (0.5% CH3CDO in 1.8 atm He). There are 3 different spectra in this figure. Bottom scan is CH3CDO heated to 1300 K; 2nd scan is CH3CDO heated to 1400 K; 3rd trace is CH3CDO heated to 1500 K.

Image of FIG. 7.
FIG. 7.

VUV (118.2 nm) photoionization mass spectra of the thermal cracking products of acetaldehyde-d3 in a pulsed reactor are shown (0.5% CD3CHO in He). There are 3 spectra in this figure. Bottom trace: CD3CHO traversing the μtubular reactor at 300 K; 2nd trace (red) is CD3CHO traversing the μtubular reactor heated to 1300 K; 3rd trace is CD3CHO traversing the μtubular reactor heated to 1500 K.

Image of FIG. 8.
FIG. 8.

An expanded spectrum of the mass range 14–20 amu for the 118.2 nm VUV photoionization of acetaldehyde-d3 is shown (0.5% CD3CHO in He). CD3CHO is heated by the pulsed μtubular reactor to 1700 K.

Image of FIG. 9.
FIG. 9.

VUV (118.2 nm) photoionization mass spectra of the thermal cracking products of acetaldehyde-d4 are shown (0.5% CD3CDO in He). Bottom trace: CD3CDO traversing the pulsed μtubular reactor at room temperature; 2nd trace (red) is CD3CDO traversing the μtubular reactor heated to 1300 K; 3rd scan is CD3CDO heated to 1500 K; 4th trace (red) is CD3CDO heated to 1600 K.

Image of FIG. 10.
FIG. 10.

Matrix IR absorption spectrum demonstrating the presence of acetylene resulting from the thermal cracking of CH3CHO at 1700 K in a pulsed reactor. The green trace is that of the buffer gas, Ar, heated to 1700 K; the narrow black spectrum is a CH3CHO at room temperature (0.1% CH3CHO in Ar); and the thick black spectrum results from heating CH3CHO to 1700 K. The two IR active vibrational modes92 of HC≡CH are assigned.

Image of FIG. 11.
FIG. 11.

Matrix IR absorption spectra demonstrating the presence of vinyl alcohol (CH2=CH–OH) following the pyrolysis of acetaldehyde in a pulsed reactor (0.1% CH3CHO in Ar). The green trace is that of the buffer gas, Ar, heated to 1700 K; the narrow black spectrum is CH3CHO at room temperature; the knotted trace (-°-°-°-) results from heating to 1400 K, the red scan is 1500 K; and the thick black spectrum results from heating CH3CHO to 1700 K. Three vibrational fundamentals for vinyl alcohol are assigned: the O–H stretch at ν1(CH2CHO–H) = 3619 cm−1, the >C=C< stretch at ν5(CH2=CHOH) = 1662 cm−1, and the H2CCHOH out-of-plane deformation at ν13(CH2CHOH) = 814 and 818 cm−1. The 817 cm−1 band in the CH3CHO room temperature spectrum is an unassigned impurity.

Image of FIG. 12.
FIG. 12.

Photoionization efficiency scans of CH3CHO that reveal the presence of vinyl alcohol (CH2=CH–OH) following the pyrolysis of acetaldehyde in a CW reactor (1% CH3CHO in Ar). The panel at the right is the PIE curve resulting from CH3CHO at 300 K and from heating to 1300 K. The IE(CH3CHO) has been measured49 to be 10.2295 ± 0.0007 eV. The panel at the left is a detailed scan of the photoionization origin. Intensity scale of 300 K scan is (0.0–0.5), while that of the 1300 K trace is (0.0–0.3). The PIE scan resulting from heating CH3CHO at 1300 K reveals a threshold consistent with that observed62 for vinyl alcohol, IE(CH2=CHOH) = 9.33 ± 0.05 eV.

Image of FIG. 13.
FIG. 13.

Matrix IR absorption spectra tracking the shifts of νOH or νOD of four vinyl alcohols that result when acetaldehyde is heated to 1700 K in a pulsed μtubular reactor. Acetaldehydes samples are 0.3% in Ar carrier gas. The green trace is that of the carrier gas, Ar, heated to 1700 K, while the purple trace is that of D2O at room temperature. In the left panel it is shown that heating CH3CHO to 1700 K (narrow black spectrum) produces CH2=CHOH, while CH3CDO (narrow red scan) yields CH2=CDOH at 1700 K. The assignments for both ν1(CH2CHO–H) = 3620 cm−1 and ν1(CH2CDO–H) = 3621 cm−1 are marked (•). In the right panel are the spectra of CD2=CHOD (thick black) resulting from pyrolyzing CD3CHO at 1700 K and CD2=CDOD (thick red) arising from heating CD3CDO at 1700 K. The assignments for both ν1(CD2CHO–D) = 2675 cm−1 and ν1(CD2CDO-D) = 2675 cm−1 are marked (•). In the right panel it is demonstrated that heating CH3CHO (the knotted trace -°-°-°-) to 1325 K shows the first appearance of ν1(CH2CHO–H).

Image of FIG. 14.
FIG. 14.

PIMS resulting from the thermal cracking of CH3CDO in a CW reactor at 1700 K; the VUV photon energy is set to 12.675 eV. Acetaldehyde sample is 0.9% in 6.6 atm He carrier gas. Figure 13 demonstrates that CH3CDO rearranges to CH2=CDOH only. This vinyl alcohol fragments to [HC≡CH, m/z 26 + HOD, m/z 19] or to [DC≡CH, m/z 27 + H2O, m/z 18]. There is a tiny signal at m/z 20 which is D2O.

Image of FIG. 15.
FIG. 15.

Thermal decomposition of CH3CDO entrained in He in a CW reactor at 1700 K; photoionization efficiency curves identify HCCH, HCCD, H2O, and HOD by their ionization thresholds. Acetaldehyde sample is 0.9% in He carrier gas.

Image of FIG. 16.
FIG. 16.

A crossover experiment to identify bimolecular reactions of (H, D) atoms with a 50:50 mixture of CH3CHO/CD3CDO. A reactant mixture of 7.45 Torr CH3CHO + 7.97 Torr CD3CDO + 5.98 Torr Xe in 1430 Torr He (0.51% CH3CHO + 0.55% CD4CDO + 0.41% Xe in He) was subjected to 1500 K and 1800 K pyrolysis by a CW μtubular reactor. The measured pressure upstream of the SiC reactor was about 71 Torr. For the experiment at 1800 K the total counts are: H2 = 2.572; HD = 10.104; D2 = 5.767. Total counts of H2 + D2 = 8.342 or 83% of total counts of HD.

Tables

Generic image for table
Table I.

Thermochemistry of CH3CHO.

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/content/aip/journal/jcp/137/16/10.1063/1.4759050
2012-10-24
2014-04-23
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Thermal decomposition of CH3CHO studied by matrix infrared spectroscopy and photoionization mass spectroscopy
http://aip.metastore.ingenta.com/content/aip/journal/jcp/137/16/10.1063/1.4759050
10.1063/1.4759050
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