A precise study of the rotational spectrum of formaldehyde H2CO, H2CO, H2CO, H2CO

The rotational spectra of formaldehyde, H₂¹²C¹⁶O and its isotopic species H₂¹³C¹⁶O, H₂¹²C¹⁸O, and H₂¹³C¹⁸O have been investigated in the ground vibrational state in the frequency region between 8 and 460 GHz. For most cases in which measurements of the a-type R- and Q-branch transitions already existed the accuracy of the line position has been improved to about 10 kHz. For H₂¹²C¹⁶O and H₂¹³C¹⁶O a large number of ΔK_a = ±2 transitions were measured with similar accuracy. These new data when combined with all other available data and appropriate weightings lead to a set of ground state parameters which for the first time are compatible with infrared and ultraviolet data. The rotational constants (and 3σ standard deviations) obtained using Watson's A-reduced Hamiltonian are:

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The microwave spectrum of cyanophosphine, H2PCN

The rotational spectra of cyanophosphine, H₂PCN, have been measured between 10 and 42.5 GHz by Fourier transform microwave spectroscopy. The rotational constants, centrifugal distortion constants, the ¹⁴N quadrupole coupling constant, and the nuclear spin-rotation coupling constants of ³¹P have been determined. Density functional ab initio calculations were performed, and the calculated values of the molecular constants are in excellent agreement with our experimentally determined results. The spectra of three isotopomers were measured, H₂P¹²C¹⁴N, H₂P¹³C¹⁴N, and H₂P¹²C¹⁵N. The derived r₀ structure is quite comparable to the ab initio predicted H₂PCN equilibrium geometry.     

The microwave spectrum of cyanophosphaacetylene, H2PCCCN

The a type transitions of the microwave rotational spectra of cyanophosphaacetylene, H₂PCCCN, have been investigated in the frequency region between 5 and 26.5 GHz by Fourier transformation microwave (FTMW) spectroscopy. Rotational, centrifugal distortion and ¹⁴N nuclear quadrupole coupling constants have been determined. Density functional theory level ab initio calculations were performed to predict the molecular constants, and the predicted values are in good agreement with our experimentally determined results. The ¹³C and ¹⁵N isotopomer transitions were also observed. The derived r₀ structure is quite comparable to the calculated H₂PCCCN equilibrium geometry.     

High resolution pure rotational spectrum of water vapor enriched by H217O and H218O

The pure rotational spectrum of a mixture of H₂¹⁶O, H₂¹⁷O and H₂¹⁸O between 50 and 730 cm^?1 was recorded on the Fourier transform spectrometer at the University of Oulu. The resolution achieved was about 0.010 cm^?1 and the precision of the unblended lines was better than 0.001 cm^?1. About 1100 lines were assigned. The measured line positions of H₂¹⁷O and H₂¹⁸O were compared with the values derived from the rotation and distortion constants given in the literature.     

The pure rotational spectrum of Difluoroiodomethane, CHF2I

The pure rotational spectrum of CHF₂I has been recorded for the first time, in a supersonic expansion in the region 1.7-17 GHz, and at room-temperature in the region 302-318 GHz. The observed transitions span the values of J^″ from 0 up to 67. Precise rotational and centrifugal distortion constants have been determined. Furthermore, the complete iodine nuclear electric quadrupole coupling tensor, in the inertial and principal axes, has been determined. Quantum chemical calculations have been performed to aid with the analysis. Iodine quadrupole mediated perturbations have resulted in the following observations: (i) several transitions having enhanced intensities and (ii) the observation of several forbidden, ΔJ=±2, transitions. Comparisons in electronic structure are made between the series of molecules CH_3-nF_nX; and X = Cl, Br, I.     

Centrifugal distortion analysis of pure rotational spectra of H216O,H217O,and H218O

Centrifugal distortion analyses based entirely on high-quality infrared data are carried out for the ground vibrational states of H₂¹⁶O, H₂¹⁷O, and H₂¹⁸O. As a result of the analyses, the values of 27 rotation and distortion constants for each species are determined. By using these constants it was possible to improve considerably the accuracy of the literature values for rotational energy levels at high J_τ, especially for H₂¹⁷O and H₂¹⁸O. The experimental values for the energy levels are deduced from the observed rotational transitions constituting the fitted data.     

H2SiCl2 中 SiH 伸缩振动的泛频光谱

在2000 ～ 9000 波数 、 12000 ～12900 波数的光谱区间记录了室温下H2SiCl2气体分子的振动泛频光谱，所用的仪器分别是高分辨傅立叶变换光谱仪和高灵敏激光腔内吸收光谱仪。用局域模模型和包含达林－丹尼生共振的简正模模型，归属了SiH伸缩振动的基频和泛频，振动量子数的改变△VSiH=1, 2, 3, 4 and 6。通过对实验能级的非线性拟合，得到SiH伸缩振动的谐振频率ωm、非谐性常数χm、键间耦合系数λ、莫尔斯振子参数 De、α 和相互作用力常数 。实验发现，随着振动能量的增加，振动簇（manifold，两个SiH键的伸缩振动量子数m+n=常数 ）中能量最低的两个能级的间距逐渐减小。当△VSiH≥4时，在实验误差范围内这两个最低的振动态能级简并。这种简并的能级结构类似双原子莫尔斯振子，符合Birge-Sponer 关系。双原子莫尔斯振子直接描述了H2SiCl2分子中SiH 的高泛频伸缩振动，表明在高振动情况下振动能量已经集中到单个SiH键上。     

The magnetic hyperfine structure in the rotational spectrum of H2CNH

The hyperfine structure in the ground-state rotational spectrum of methanimine was studied in the frequency range of 64-172 GHz by means of the Lamb-dip technique. This allowed to resolve, in some hyperfine components due to the ¹⁴N nucleus, doublets separated by only some tenth of kHz. We explain the splittings as due to magnetic interactions of the three protons with their molecular environment. The analysis of the experimental spectrum has been guided by quantum-chemical calculations of the hyperfine parameters.     

A precise study of the rotational spectrum of formaldehyde H212C16O,H213C16O,H212C18O,H213C18O

The rotational spectra of formaldehyde, H₂¹²C¹⁶O and its isotopic species H₂¹³C¹⁶O, H₂¹²C¹⁸O, and H₂¹³C¹⁸O have been investigated in the ground vibrational state in the frequency region between 8 and 460 GHz. For most cases in which measurements of the a-type R- and Q-branch transitions already existed the accuracy of the line position has been improved to about 10 kHz. For H₂¹²C¹⁶O and H₂¹³C¹⁶O a large number of ΔK_a = ±2 transitions were measured with similar accuracy. These new data when combined with all other available data and appropriate weightings lead to a set of ground state parameters which for the first time are compatible with infrared and ultraviolet data. The rotational constants (and 3σ standard deviations) obtained using Watson's A-reduced Hamiltonian are:

     

11.

Carbon-13 Isotopic Species of H₂C₃, H₂C₄, and H₂C₅: High-Resolution Rotational Spectra     

M.C. McCarthyP. Thaddeus 《Journal of Molecular Spectroscopy》2002,211(2):235-240

The microwave rotational spectra of the carbon-13 isotopic species of H₂C₃, H₂C₄, and H₂C₅ have been observed in a pulsed supersonic molecular beam by Fourier transform microwave spectroscopy. At high resolution all of the rotational lines exhibit hyperfine structure produced by the magnetic interaction between the nuclear spin of ¹³C and the overall rotation of the molecule. The component of the nuclear spin-rotation tensor along the a-inertial axis is large for most isotopic species, especially at the carbene carbon; at this position C_aa is two to three times larger than at other substituted positions along the chain. In contrast to both H₂C₃ and H₂C₃, in H₂C₄C_aa exhibits a pronounced alternation along the carbon chain backbone. Following detection of the five carbon-13 isotopic species and D₂C₅, an experimental structure (r₀) has been determined to high accuracy for H₂C₅.     

12.

RHEED and Auger study of the MoO₃(010) surface interaction with H₂S/H₂ mixture and pure H₂S     

A. Steinbrunn  C. Lattaud 《Surface science》1985,155(1):279-295

Pure single crystals of MoO₃ were carefully grown by physical vapor transport. The initial stages of the interaction of H₂S with a MoO₃ (010) surface were studied by RHEED and AES at low pressure p <133 Pa and at T < 700 K. Three main stages were found: (a) The formation of either a completely disordered sulphur adiayer (with pure H₂S) or a superstructure MoO₃(010)-[2 × 1]S (with H₂S/H₂). (b) A reduction of MoO₃ producing oriented three-dimensional MoO₂ islands, (c) An epitaxial overgrowth of MoS₂ from the MoO₂ three-dimensional crystallites.     

13.

Absorption spectrum of BS₂ at 4°K     

J.M. Brom  W. Weltner 《Journal of Molecular Spectroscopy》1973,45(1):82-98

BS₂, trapped in neon matrices at 4°K, exhibits extensive progressions in the A²Π_u ← X²Π_g and $\text{B}{}^2\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}\text{← X}{}^2\text{Π}{}_{\mathrm{g}}$ systems. From these transitions, those observed in the infrared, and a reinterpretation of gas-phase data, the following molecular constants (in solid neon) are obtained for linear symmetric ¹¹BS₂ (in cm^?1):

	H212C16O	H213C16O	H212C18O	H213C18O
A/MHz	281 970.572 (24)	281 993.258(135)	281 961.94 (39)	281 985.00 (93)
B/MHz	38 836.0456(13)	37 811.0887(25)	36 904.1693(66)	35 859.256(10)
C/MHz	34 002.2034(12)	33 213.9790(25)	32 511.5311(63)	31 697.868(10)

     

14.

Spin wave spectrum of Ca₂MnO₄ at 4.2K     

B. Hennion  F. Moussa  G. Pepy  G. Ollivier 《Solid State Communications》1973,13(7):919-922

The spin-wave spectrum of Ca₂MnO₄ has been measured at 4.2K. It can be fully built from two exchange integrals in the (001) plane $\text{J}{}_{\mathrm{<mtext>1</mtext>}}\text{=}\text{5.9}$ meV and $\text{J}{}_{\mathrm{<mtext>2=1.7\; meV</mtext>}}$, and in out-of plane exchange integral $\text{J}\text{′}{}_{\mathrm{<mtext>1</mtext>}}\text{=}\text{0.6}\text{meV}$. This latter explains quite well the splitting of the magnon dispersion curve.     

15.

Spectroscopically determined potential energy surfaces of the H₂O, H₂O, and H₂O isotopologues of water     

Sergei V. Shirin  Oleg L. Polyansky  Nikolai F. Zobov  Roman I. Ovsyannikov  Jonathan Tennyson 《Journal of Molecular Spectroscopy》2006,236(2):216-223

Adiabatic potential energy surfaces (PESs) for three major isotopologues of water, H₂¹⁶O, H₂¹⁷O, and H₂¹⁸O, are constructed by fitting to observed vibration-rotation energy levels of the system using the nuclear motion program DVR3D employing an exact kinetic energy operator. Extensive tests show that the mass-dependent ab initio surfaces due to Polyansky et al. [O.L. Polyansky, A.G. Császár, S.V. Shirin, N.F. Zobov, P. Barletta, J. Tennyson, D.W. Schwenke, P.J. Knowles, Science 299 (2003) 539-542.] provide an excellent starting point for the fits. The refinements are performed using a mass-independent morphing function, which smoothly distorts the original adiabatic ab initio PESs. The best overall fit is based on 1788 experimental energy levels with the rotational quantum number J = 0, 2, and 5. It reproduces these levels with a standard deviation of 0.079 cm⁻¹ and gives, when explicit allowance is made for nonadiabatic rotational effects, excellent predictions for levels up to J = 40. Theoretical linelists for all three isotopologues of water involved in the PES construction were calculated up to 26 000 cm⁻¹ with energy levels up to J = 10. These linelists should make an excellent starting point for spectroscopic modelling and analysis.     

16.

The adsorption of CO,H₂, H₂, CO₂ and H₂O on carburized and graphitized Ni(110)     

J.G. McCarty  R.J. Madix 《Surface science》1976,54(1):121-138

A study of the adsorption/desorption behavior of CO, H₂O, CO₂ and H₂ on Ni(110)(4 × 5)-C and Ni(110)-graphite was made in order to assess the importance of desorption as a rate-limiting step for the decomposition of formic acid and to identify available reaction channels for the decomposition. The carbide surface adsorbed CO and H₂O in amounts comparable to the clean surface, whereas this surface, unlike clean Ni(110), did not appreciably adsorb H₂. The binding energy of CO on the carbide was coverage sensitive, decreasing from 21 to 12 $\text{kcal}\text{mol}$ as the CO coverage approached 1.1 × 10¹⁵ molecules cm^?2 at 200K. The initial sticking probability and maximum coverage of CO on the carbide surface were close to that observed for clean Ni(110). The amount of H₂, CO, CO₂ and H₂O adsorbed on the graphitized surface was insignificant relative to the clean surface. The kinetics of adsorption/desorption of the states observed are discussed.     

17.

The H₂O spectrum between 4200 and 5000 cm⁻¹     

J.-M. Flaud  C. Camy-Peyret  J.-P. Maillard  G. Guelachvili 《Journal of Molecular Spectroscopy》1977,65(2):219-228

The spectrum of water vapor heated in an absorption cell at 60°C has been recorded on a Fourier transform spectrometer between 4200 and 5000 cm^?1. A thorough analysis of the spectrum has been performed, leading to an improved and extended set of rotational energy levels for the (030) vibrational state. Intensities of about 50 lines of the 3ν₂ band are reported and a calculation of these intensities has been performed allowing the determination of the vibrational matrix element of the transformed dipole moment operator.     

18.

Reaction products from a discharge of N₂ and H₂S: The microwave spectrum of NH₂SH     

F. J. Lovas  R. D. Suenram  W. J. Stevens 《Journal of Molecular Spectroscopy》1983,100(2):316-331

Thiohydroxylamine has been identified as one of the reaction products from the discharge reaction of N₂ + H₂S. Both cis and trans conformers have been observed. The rotational spectra have been studied from 56 to 170 GHz for the normal species and several deuterated isotopic species of each conformer. The electric dipole moments of both conformers have been determined. A number of the transitions of the cis conformer exhibit splittings due to the nuclear quadrupole moment of the ¹⁴N nucleus. A least squares fit of the frequency splittings have led to an analysis of the eQq values. Ab initio calculations using a 4-31G basis set both with and without polarization functions have been carried out to aid in the analysis and to provide a final structural comparison with the microwave results.     

19.

Experimental and numerical investigation of hetero-/homogeneous combustion of CO/H₂/O₂/N₂ mixtures over platinum at pressures up to 5 bar     

Yohannes Ghermay  John Mantzaras  Rolf Bombach 《Proceedings of the Combustion Institute》2011,33(2):1827-1835

The hetero-/homogeneous combustion of fuel-lean CO/H₂/O₂/N₂ mixtures over platinum is investigated at pressures up to 5 bar, inlet temperatures (T_IN) up to 874 K, and a constant CO:H₂ molar ratio of 2:1. Experiments are performed in an optically accessible channel-flow catalytic reactor and involve planar laser induced fluorescence (LIF) of the OH radical for the assessment of homogeneous (gas-phase) ignition and 1-D Raman measurements of major gas-phase species concentrations over the catalyst boundary layer for the evaluation of the heterogeneous (catalytic) processes. Simulations are carried out with an elliptic 2-D model that includes detailed heterogeneous and homogeneous chemical reaction schemes. The predictions reproduce the Raman-measured catalytic CO and H₂ consumption, and it is further shown that for wall temperatures in the range 975 ? T_w ? 1165 K the heterogeneous pathways of CO and H₂ are largely decoupled. However, for wall temperatures below a limiting value of 710–720 K and for the range of pressures and mixture preheats investigated, CO(s) blockage of the surface inhibits the catalytic conversion of both fuel components. The homogeneous ignition distance is well-reproduced by the model for T_IN > 426 K, but it is modestly overpredicted at lower T_IN. Possible reasons for these modest differences can be the values of third body efficiencies in the gas-phase reaction mechanism. The sensitivity of homogeneous ignition distance on the catalytic reactions is weak, while the H₂/O₂ subset of the CO/H₂/O₂ gaseous reaction mechanism controls the onset of homogeneous ignition. Pure hydrogen hetero-/homogeneous combustion results in flames established very close to the catalytic walls. However, in the presence of CO the gaseous combustion of hydrogen extends well-inside the channel core, thus allowing homogeneous consumption of H₂ at considerably shorter reactor lengths. Finally, implications of the above findings for the design of syngas-based catalytic reactors for power generation systems are discussed.     

20.

Observation of hot bands in the infrared spectrum of H₂CO     

Ricardo Perez  Yurii Utkin  Jiaxiang Han  Robert F. Curl 《Journal of Molecular Spectroscopy》2006,236(2):151-157

Two hot bands in the infrared spectrum of formaldehyde (H₂CO) have been identified by means of tunable infrared laser spectroscopy using a jet-cooled sample. One band falls in the region 2760-2800 cm⁻¹; it follows a-type selection rules and it has been assigned as the ν₁ + ν₄ − ν₄ hot band. The other band falls in the region 2800-2860 cm⁻¹; it follows b-type selection rules and it has been assigned as the ν₅ + ν₄ − ν₄ hot band. The observations are restricted to low J and K_a levels. It has consequently been possible to ignore the effects of the extensive Coriolis couplings involving these levels in the analysis of the spectra and to model the rotational structure as that of a simple asymmetric top. Least-squares fits of the data have provided values for the band origins: 2774.2706(11) cm⁻¹ for the ν₁ + ν₄ − ν₄ and 2829.2621(8) cm⁻¹ for the ν₅ + ν₄ − ν₄ band. Term values for the upper vibrational levels involved in the transitions have been determined by use of the previously reported term values for the v₄ = 1 level.     

$\text{B}{}^2\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}$	T0 = 24,072	$\text{ν}{}_1\text{= 516}$
$\text{A}{}^2\text{Π}{}_{\mathrm{u}}$	T0 = 13.766	$\text{ν}{}_1\text{= 506}$
	A0 = ?263	$\text{ν}{}_2\text{= 311}$
		$\text{ν}{}_3\text{= 1535}$
$\text{X}{}^2\text{Π}{}_{\mathrm{g}}$	A0 = ?440	$\text{ν}{}_1\text{= 510}$
		$\text{ν}{}_2\text{= ～120}$
		$\text{ν}{}_3\text{= 1015}$

Carbon-13 Isotopic Species of H2C3, H2C4, and H2C5: High-Resolution Rotational Spectra

The microwave rotational spectra of the carbon-13 isotopic species of H₂C₃, H₂C₄, and H₂C₅ have been observed in a pulsed supersonic molecular beam by Fourier transform microwave spectroscopy. At high resolution all of the rotational lines exhibit hyperfine structure produced by the magnetic interaction between the nuclear spin of ¹³C and the overall rotation of the molecule. The component of the nuclear spin-rotation tensor along the a-inertial axis is large for most isotopic species, especially at the carbene carbon; at this position C_aa is two to three times larger than at other substituted positions along the chain. In contrast to both H₂C₃ and H₂C₃, in H₂C₄C_aa exhibits a pronounced alternation along the carbon chain backbone. Following detection of the five carbon-13 isotopic species and D₂C₅, an experimental structure (r₀) has been determined to high accuracy for H₂C₅.     

RHEED and Auger study of the MoO3(010) surface interaction with H2S/H2 mixture and pure H2S

Pure single crystals of MoO₃ were carefully grown by physical vapor transport. The initial stages of the interaction of H₂S with a MoO₃ (010) surface were studied by RHEED and AES at low pressure p <133 Pa and at T < 700 K. Three main stages were found: (a) The formation of either a completely disordered sulphur adiayer (with pure H₂S) or a superstructure MoO₃(010)-[2 × 1]S (with H₂S/H₂). (b) A reduction of MoO₃ producing oriented three-dimensional MoO₂ islands, (c) An epitaxial overgrowth of MoS₂ from the MoO₂ three-dimensional crystallites.     

Absorption spectrum of BS2 at 4°K

BS₂, trapped in neon matrices at 4°K, exhibits extensive progressions in the A²Π_u ← X²Π_g and $\text{B}{}^2\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}\text{← X}{}^2\text{Π}{}_{\mathrm{g}}$ systems. From these transitions, those observed in the infrared, and a reinterpretation of gas-phase data, the following molecular constants (in solid neon) are obtained for linear symmetric ¹¹BS₂ (in cm^?1):

Spin wave spectrum of Ca2MnO4 at 4.2K

The spin-wave spectrum of Ca₂MnO₄ has been measured at 4.2K. It can be fully built from two exchange integrals in the (001) plane $\text{J}{}_{\mathrm{<mtext>1</mtext>}}\text{=}\text{5.9}$ meV and $\text{J}{}_{\mathrm{<mtext>2=1.7\; meV</mtext>}}$, and in out-of plane exchange integral $\text{J}\text{′}{}_{\mathrm{<mtext>1</mtext>}}\text{=}\text{0.6}\text{meV}$. This latter explains quite well the splitting of the magnon dispersion curve.     

Spectroscopically determined potential energy surfaces of the H2O, H2O, and H2O isotopologues of water

Adiabatic potential energy surfaces (PESs) for three major isotopologues of water, H₂¹⁶O, H₂¹⁷O, and H₂¹⁸O, are constructed by fitting to observed vibration-rotation energy levels of the system using the nuclear motion program DVR3D employing an exact kinetic energy operator. Extensive tests show that the mass-dependent ab initio surfaces due to Polyansky et al. [O.L. Polyansky, A.G. Császár, S.V. Shirin, N.F. Zobov, P. Barletta, J. Tennyson, D.W. Schwenke, P.J. Knowles, Science 299 (2003) 539-542.] provide an excellent starting point for the fits. The refinements are performed using a mass-independent morphing function, which smoothly distorts the original adiabatic ab initio PESs. The best overall fit is based on 1788 experimental energy levels with the rotational quantum number J = 0, 2, and 5. It reproduces these levels with a standard deviation of 0.079 cm⁻¹ and gives, when explicit allowance is made for nonadiabatic rotational effects, excellent predictions for levels up to J = 40. Theoretical linelists for all three isotopologues of water involved in the PES construction were calculated up to 26 000 cm⁻¹ with energy levels up to J = 10. These linelists should make an excellent starting point for spectroscopic modelling and analysis.     

The adsorption of CO,H2, H2, CO2 and H2O on carburized and graphitized Ni(110)

A study of the adsorption/desorption behavior of CO, H₂O, CO₂ and H₂ on Ni(110)(4 × 5)-C and Ni(110)-graphite was made in order to assess the importance of desorption as a rate-limiting step for the decomposition of formic acid and to identify available reaction channels for the decomposition. The carbide surface adsorbed CO and H₂O in amounts comparable to the clean surface, whereas this surface, unlike clean Ni(110), did not appreciably adsorb H₂. The binding energy of CO on the carbide was coverage sensitive, decreasing from 21 to 12 $\text{kcal}\text{mol}$ as the CO coverage approached 1.1 × 10¹⁵ molecules cm^?2 at 200K. The initial sticking probability and maximum coverage of CO on the carbide surface were close to that observed for clean Ni(110). The amount of H₂, CO, CO₂ and H₂O adsorbed on the graphitized surface was insignificant relative to the clean surface. The kinetics of adsorption/desorption of the states observed are discussed.     

The H2O spectrum between 4200 and 5000 cm−1

The spectrum of water vapor heated in an absorption cell at 60°C has been recorded on a Fourier transform spectrometer between 4200 and 5000 cm^?1. A thorough analysis of the spectrum has been performed, leading to an improved and extended set of rotational energy levels for the (030) vibrational state. Intensities of about 50 lines of the 3ν₂ band are reported and a calculation of these intensities has been performed allowing the determination of the vibrational matrix element of the transformed dipole moment operator.     

Reaction products from a discharge of N2 and H2S: The microwave spectrum of NH2SH

Thiohydroxylamine has been identified as one of the reaction products from the discharge reaction of N₂ + H₂S. Both cis and trans conformers have been observed. The rotational spectra have been studied from 56 to 170 GHz for the normal species and several deuterated isotopic species of each conformer. The electric dipole moments of both conformers have been determined. A number of the transitions of the cis conformer exhibit splittings due to the nuclear quadrupole moment of the ¹⁴N nucleus. A least squares fit of the frequency splittings have led to an analysis of the eQq values. Ab initio calculations using a 4-31G basis set both with and without polarization functions have been carried out to aid in the analysis and to provide a final structural comparison with the microwave results.     

Experimental and numerical investigation of hetero-/homogeneous combustion of CO/H2/O2/N2 mixtures over platinum at pressures up to 5 bar

The hetero-/homogeneous combustion of fuel-lean CO/H₂/O₂/N₂ mixtures over platinum is investigated at pressures up to 5 bar, inlet temperatures (T_IN) up to 874 K, and a constant CO:H₂ molar ratio of 2:1. Experiments are performed in an optically accessible channel-flow catalytic reactor and involve planar laser induced fluorescence (LIF) of the OH radical for the assessment of homogeneous (gas-phase) ignition and 1-D Raman measurements of major gas-phase species concentrations over the catalyst boundary layer for the evaluation of the heterogeneous (catalytic) processes. Simulations are carried out with an elliptic 2-D model that includes detailed heterogeneous and homogeneous chemical reaction schemes. The predictions reproduce the Raman-measured catalytic CO and H₂ consumption, and it is further shown that for wall temperatures in the range 975 ? T_w ? 1165 K the heterogeneous pathways of CO and H₂ are largely decoupled. However, for wall temperatures below a limiting value of 710–720 K and for the range of pressures and mixture preheats investigated, CO(s) blockage of the surface inhibits the catalytic conversion of both fuel components. The homogeneous ignition distance is well-reproduced by the model for T_IN > 426 K, but it is modestly overpredicted at lower T_IN. Possible reasons for these modest differences can be the values of third body efficiencies in the gas-phase reaction mechanism. The sensitivity of homogeneous ignition distance on the catalytic reactions is weak, while the H₂/O₂ subset of the CO/H₂/O₂ gaseous reaction mechanism controls the onset of homogeneous ignition. Pure hydrogen hetero-/homogeneous combustion results in flames established very close to the catalytic walls. However, in the presence of CO the gaseous combustion of hydrogen extends well-inside the channel core, thus allowing homogeneous consumption of H₂ at considerably shorter reactor lengths. Finally, implications of the above findings for the design of syngas-based catalytic reactors for power generation systems are discussed.     

Observation of hot bands in the infrared spectrum of H2CO

Two hot bands in the infrared spectrum of formaldehyde (H₂CO) have been identified by means of tunable infrared laser spectroscopy using a jet-cooled sample. One band falls in the region 2760-2800 cm⁻¹; it follows a-type selection rules and it has been assigned as the ν₁ + ν₄ − ν₄ hot band. The other band falls in the region 2800-2860 cm⁻¹; it follows b-type selection rules and it has been assigned as the ν₅ + ν₄ − ν₄ hot band. The observations are restricted to low J and K_a levels. It has consequently been possible to ignore the effects of the extensive Coriolis couplings involving these levels in the analysis of the spectra and to model the rotational structure as that of a simple asymmetric top. Least-squares fits of the data have provided values for the band origins: 2774.2706(11) cm⁻¹ for the ν₁ + ν₄ − ν₄ and 2829.2621(8) cm⁻¹ for the ν₅ + ν₄ − ν₄ band. Term values for the upper vibrational levels involved in the transitions have been determined by use of the previously reported term values for the v₄ = 1 level.