CH4 Reaction Research Articles

C-H Bond Activation by the Excited Zinc Atom: Gas-Phase Formation of Methylzinc Hydride (HZnCH3) Based on Multireference Second-Order Perturbation Theory and Coupled Cluster Calculations.

The pioneering spectroscopic observations of the methylzinc hydride [HZnCH3(X1A1)] molecule were reported previously by the Ziurys group [J. Am. Chem. Soc.2010, 132, 17186–17192], and the possible formation mechanisms were suggested therein, including those with the participation of excited zinc atoms in reaction with methane. Herein, the ground singlet state and the lowest excited triplet state potential energy surfaces of the Zn + CH4 reaction have been explored using high-level electronic structure calculations with multireference second-order perturbation theory and coupled cluster singles and doubles with perturbative triples (CCSD(T)) methods in conjunction with all-electron basis sets (up to aug-cc-pV5Z) and scalar relativistic effects incorporated via the second-order Douglas–Kroll–Hess (DK) method. Based on the ab initio results, a plausible scenario for the formation of HZnCH3(X1A1) is proposed involving the activation of the C–H bond of methane by the lowest excited 3P state atomic zinc. Calculations also highlight the importance of an agostic-like Zn···H–C interactions in the pre-activation complex and good agreement between the structure of the HZnCH3(X1A1) molecule predicted at the DK-CCSD(T)/aug-cc-pVQZ-DK level of theory and that derived from rotational spectroscopy, as well as the discrepancies between the ab initio and density functional theory predictions.

Study of effects of ammonia addition on soot formation characteristics in n-heptane co-flow laminar diffusion flames

Ammonia is a compelling carbon-free fuel, and co-firing ammonia with conventional hydrocarbon fuels receives growing interest as a feasible solution to mitigate CO2 emission. This study experimentally and numerically investigated the soot formation characteristics of n-heptane co-flow laminar diffusion flames with different contents of ammonia (up to 40% by volume, balanced using argon). The soot volume fraction (SVF) in the flames was quantitatively measured via laser-induced incandescence technique; PAHs and OH radical were qualitatively determined via laser-induced fluorescence technique. Results showed that ammonia addition reduced the SVF, i.e., a peak SVF decrease of 35% at 40% ammonia. Meanwhile, PAH content also decreased with ammonia addition, demonstrating that ammonia would effectively inhibit the formation of PAHs. Thus, the inception and growth of soot decreased. Interestingly, OH radical was reduced with ammonia addition, revealing that ammonia also chemically inhibited soot oxidation. The results confirmed that ammonia reduced the soot loading in the flames due to inhibitory effect on the inception and growth of soot rather than the enhancement on oxidation. The established mechanism effectively captured the variation of different PAHs in the experiments. Numerical analysis showed that the formation of the first aromatic ring benzene was reduced by ammonia as a result of the reduction of C4H5 and R203:C4H5+C2H2 reaction. In addition, the reduced hydrogen abstraction due to decrease in H, coupled with the reduced small PAH, led to the decrease in PAH growth. Nevertheless, a more comprehensive mechanism including the reactions between aromatics and nitrogen species, such as NH, CN, and NOx, is still required in future studies.

A comprehensive experimental and kinetic modeling study of dimethoxymethane combustion

Dimethoxymethane (DMM, CH3OCH2OCH3), the simplest member in the class of polyoxymethylene dimethyl ethers (PODE), is regarded as a promising fuel substitute for compression ignition engines. To better understand its combustion characteristics, a comprehensive experimental and kinetic modeling study on the combustion of DMM was conducted. Ignition delay times (IDTs) of DMM/O2/Ar mixtures were measured in a shock tube at pressures from 1.0 to 10 atm, for temperatures from 1050 to 1450 K, and equivalence ratios of 0.5, 1.0 and 2.0. A predominantly ab initio derived detailed kinetic model of DMM with 121 species and 646 reactions was developed based on AramcoMech2.0 with an updated sub-mechanism of methyl formate (MF, CH3OCHO). CO bond fissions occurred in CH2O and CH3O moieties were demonstrated to be the dominating reaction pathways in DMM high temperature chemistry rather than the competing non-radical decomposition channels. Flux and sensitivity analyses indicated that the two CO bond fissions have a comparatively promoting effect on reactivity, while the DMM = CH3OCH2O + CH3 reaction was the dominating channel at high temperatures. The proposed model was also validated against literature experimental data, including ignition delay times, jet stirred reactor species concentrations, laminar pre-mixed flame speciation, laminar burning velocities and plug-flow reactor speciation. The good performance of the proposed model for reproducing these data revealed its ability to predict DMM combustion over a wide range of conditions. Major reaction pathways of DMM could also apply to larger PODE compounds.

Study the Mechanism of Formation of Different Products of the Reaction Between Propargyl and Methyl Radicals

The mechanism of the reaction between propargyl radical (C3H3) and methyl radical (CH3) has been studied by the quantum chemical method using the M06-2X functional in conjunction with the aug-cc-pVTZ basis set. The potential energy surface (PES) for the C3H3 + CH3 system has been established. The calculated results indicate that the C3H3 + CH3 reaction has two main entrance channels leading to two stabilized intermediates, buta-1,2-diene and but-1-yne, which become the major intermediate products of the reaction system. From these two intermediate states, 19 different bimolecular products can be formed. For which, C2H2 + C2H4 is the most thermodynamically favorable product.

Insight into temperature impact of Ta filaments on high-growth-rate diamond (100) films by hot-filament chemical vapor deposition

To improve the growth rate of diamond films, we grew single-crystalline (100) diamond films by hot-filament chemical vapor deposition (HFCVD), and investigated their growth mechanism. The methane/hydrogen concentration (CH4/H2) dependence of the growth rate was evaluated at a filament temperature of 3000 °C. The growth rate reached 17.9 μm/h at CH4/H2 = 5% and saturated at higher CH4/H2. We then investigated the filament-temperature dependence of the CH4 reaction rate at CH4/H2 = 5% (at which the methane supply is sufficient). The growth rate decreased with inverse filament temperature, indicating that the growth rate is governed by reactions on the filament surface. From the Arrhenius plot, the activation energy of diamond growth was estimated as 440 kJ/mol, close to that of CH4 → CH3⁎ + H⁎ decomposition. This result indicates that decomposition of CH4 and the formation of CH3 by the filament surface affect the growth rate of HFCVD-grown diamond.

Transformation of an Embedded Five-Membered Ring in Polycyclic Aromatic Hydrocarbons via the Hydrogen-Abstraction-Acetylene-Addition Mechanism: A Theoretical Study.

Five-membered rings are constituents of many polycyclic aromatic hydrocarbons (PAHs), and their presence on the edges of large PAHs has been repeatedly observed experimentally. However, modern kinetic combustion models often do not consider the growth of PAHs through the transformation of the five-membered rings. In connection with the above, we carried out a theoretical study of the mechanism of hydrogen-abstraction-acetylene-addition (HACA) transformation of an embedded five-membered ring on the armchair PAH edge to a six-membered ring, considering cyclopenta[d,e,f]phenanthrene (4,5-methylenephenanthrene) as a prototype system for this process. The potential energy surface for the reactions of cyclopenta[d,e,f]phenanthrenyl radicals produced by direct H abstractions from cyclopenta[d,e,f]phenanthrene with acetylene has been compiled at the G3(MP2,CC)//B3LYP/6-311G(d,p) level of theory including zero-point vibrational energy corrections. The computed energies and molecular parameters were then used to solve the Rice-Ramsperger-Kassel-Marcus master equation in order to calculate the reaction rate at various pressures and temperatures, which were fitted to the modified Arrhenius equation for further kinetic modeling. The results show that the HACA transformation of the embedded five-membered ring to a six-membered ring is possible, albeit slow. The most viable reaction mechanism involves the R2 + C2H2 reaction, where the acetylene molecules add to a σ-radical in the six-membered ring adjacent to the five-membered ring via a low entrance barrier. The predominant product of R2 + C2H2 is predicted to be 3-ethynyl-4H-cyclopenta[def]phenanthrene Pr5 via immediate H elimination from the initial addition complex. Next, Pr5 undergoes H-assisted isomerization to 4aH-pentaleno[4,3,2,1-cdef]phenanthrene Pr4, and the latter adds a H-atom eventually forming the 1-pyrenylmethyl radical Pr3: R2 + C2H2 ⇆ 3-ethynyl-4H-cyclopenta[def]phenanthrene (Pr5) + H or 4aH-pentaleno[4,3,2,1-cdef]phenanthrene (Pr4) + H; Pr5 + H ⇆ Pr4 + H; Pr4 + H → 1-pyrenylmethyl (Pr3). This HACA sequence may be competitive with the methyl radical addition to the R1 radical formed by H abstraction from the CH2 group in the five-membered ring of cyclopenta[d,e,f]phenanthrene, which provides a pathway to pyrene following two H-atom losses. Relative contributions of the two mechanisms of the five- to six-membered ring transformation would strongly depend on the branching ratios of the R1 and R2 radicals produced by the H abstractions and the available concentration of C2H2 versus CH3 and hence differ in different flames.

High Active Co/Mg1-xCex3+O Catalyst: Effects of Metal-Support Promoter Interactions on CO2 Reforming of CH4 Reaction

Co/Mg1−XCe3+XO (x = 0, 0.03, 0.07, 0.15; 1 wt% cobalt each) catalysts for the dry reforming of methane (DRM) reaction were prepared using the co-precipitation method with K2CO3 as precipitant. Characterization of the catalysts was achieved by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (H2-TPR), Brunauer–Emmett–Teller (BET), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA). The role of several reactant and catalyst concentrations, and reaction temperatures (700–900 °C) on the catalytic performance of the DRM reaction was measured in a tubular fixed-bed reactor under atmospheric pressure at various CH4/CO2 concentration ratios (1:1 to 2:1). Using X-ray diffraction, a surface area of 19.2 m2.g−1 was exhibited by the Co/Mg0.85Ce3+0.15O catalyst and MgO phase (average crystallite size of 61.4 nm) was detected on the surface of the catalyst. H2 temperature programmed reaction revealed a reduction of CoO particles to metallic Co0 phase. The catalytic stability of the Co/Mg0.85Ce3+0.15O catalyst was achieved for 200 h on-stream at 900 °C for the 1:1 CH4:CO2 ratio with an H2/CO ratio of 1.0 and a CH4, CO2 conversions of 75% and 86%, respectively. In the present study, the conversion of CH4 was improved (75%–84%) when conducting the experiment at a lower flow of oxygen (1.25%). Finally, the deposition of carbon on the spent catalysts was analyzed using TEM and Temperature programmed oxidation-mass spectroscopy (TPO-MS) following 200 h under an oxygen stream. Better anti-coking activity of the reduced catalyst was observed by both, TEM, and TPO-MS analysis. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Theoretical studies on CH4 combustion in O2/H2O atmosphere

The hydroxyl radical reactions are of extremely significant in combustion chemistry. Direct dynamics simulations are used to study the atomic-level mechanisms of OH(H2O)n + CH4 (n = 0,1,2) reactions starting from the [(H2O)nOH---H---CH3] central barrier, which is the important step in the combustion of CH4 in an O2/H2O environment. The simulation results show the propensity for the solvated products due to the thermodynamic preference and the stability of water cluster in products. Although there is a deep minimum (H2O)nH2O---CH3 complex in the product exit channel on potential energy surface, the majority of the trajectories avoided this well and instead directly dissociated to products, showing a non-IRC behavior. Significantly, with the addition of two water molecules, the reaction probability, and thus the reaction rate constant increases compared to the one hydrated reaction. This study provides an understanding of CH4 combustion in O2/H2O atmosphere.

Kinetics of the Reactions of Methyl Radical with Hydrogen, Methyl and Ethyl Peroxides

AbstractThe HOOH+CH3, CH3OOH+CH3 and CH3CH2OOH+CH3 reactions were characterized using accurate ab initio methods with reliable basis sets. The reaction rate constants were calculated by canonical variational transition state theory as applied to a complex mechanism involving the formation of reactant complexes. The formation of aldehyde or formaldehyde was observed when the CH3 radical attacks on the CH2 group in CH3CH2OOH or on the CH3 group in CH3OOH. The results showed that the channels of H‐abstraction from OH group are dominant channels at low temperature, while the channels of OH‐transfer to CH3 become predominant with increasing temperature. For the CH3OOH+CH3 reaction, the channel producing CH2O+OH and the OH‐transfer channel have a similar rate coefficient.

Conversion reactions in atomic layer processing with emphasis on ZnO conversion to Al2O3 by trimethylaluminum

Atomic layer processing such as atomic layer deposition (ALD) and thermal atomic layer etching (ALE) is usually described in terms of sequential, self-limiting surface reactions. This picture for ALD and thermal ALE leaves out the possibility that the metal precursor in ALD and thermal ALE can also convert the surface material to another new material. This perspective introduces the previous evidence for conversion reactions in atomic layer processing based on a variety of studies, including Al2O3 ALD on ZnO, growth of Zn(O,S) alloys, “self-cleaning” of III-V semiconductor surfaces, and thermal ALE of ZnO and SiO2. The paper then focuses on the reaction of Al(CH3)3 [trimethylaluminum (TMA)] on ZnO as a model conversion system. A variety of techniques are utilized to monitor ZnO conversion to Al2O3 using TMA at 150 °C. These techniques include FTIR spectroscopy, quadrupole mass spectrometry (QMS), x-ray reflectivity (XRR), gravimetric analysis, x-ray photoelectron spectroscopy (XPS), and quartz crystal microbalance (QCM) measurements. The various studies focus on ZnO conversion to Al2O3 for both hydroxyl-terminated and ethyl-terminated ZnO substrates. FTIR studies observed the conversion of ZnO to Al2O3 and provided evidence that the conversion is self-limiting at higher TMA exposures. QMS studies identified the volatile reaction products during the TMA reaction with ZnO as CH4, C2H4, C2H6, and Zn(CH3)2. The CH4 reaction product preceded the appearance of the Zn(CH3)2 reaction product. XRR investigations determined that the thickness of the Al2O3 conversion layer on ZnO limits at ∼1.0 nm at 150 °C after larger TMA exposures. A gravimetric analysis of the conversion reaction on ZnO nanoparticles with a diameter of 10 nm displayed a percent mass loss of ∼49%. This mass loss is consistent with an Al2O3 shell of ∼1 nm on a ZnO core with a diameter of ∼6 nm. XPS studies revealed that ZnO ALD films with a thickness of 2 nm were almost completely converted to Al2O3 by large TMA exposures at 150 °C. QCM investigations then measured the mass changes for lower TMA exposures on hydroxyl-terminated and ethyl-terminated ZnO films. More mass loss was observed on ethyl-terminated ZnO films compared with hydroxyl-terminated films, because TMA does not have the possibility of reacting with hydroxyl groups on ethyl-terminated ZnO films. The mass losses also increased progressively with temperatures ranging from 100 to 225 °C on both hydroxyl-terminated and ethyl-terminated ZnO films. The perspective concludes with a discussion of the generality of conversion reactions in atomic layer processing.

Catalytic Reaction of Carbon Dioxide with Methane on Supported Noble Metal Catalysts

The conversion of CO2 and CH4, the main components of the greenhouse gases, into synthesis gas are in the focus of academic and industrial research. In this review, the activity and stability of different supported noble metal catalysts were compared in the CO2 + CH4 reaction on. It was found that the efficiency of the catalysts depends not only on the metal and on the support but on the particle size, the metal support interface, the carbon deposition and the reactivity of carbon also influences the activity and stability of the catalysts. The possibility of the activation and dissociation of CO2 and CH4 on clean and on supported noble metals were discussed separately. CO2 could dissociate on metal surfaces, this reaction could proceed via the formation of carbonate on the support, or on the metal–support interface but in the reaction the hydrogen assisted dissociation of CO2 was also suggested. The decrease in the activity of the catalysts was generally attributed to carbon deposition, which can be formed from CH4 while others suggest that the source of the surface carbon is CO2. Carbon can occur in different forms on the surface, which can be transformed into each other depending on the temperature and the time elapsed since their formation. Basically, two reaction mechanisms was proposed, according to the mono-functional mechanism the activation of both CO2 and CH4 occurs on the metal sites, but in the bi-functional mechanism the CO2 is activated on the support or on the metal–support interface and the CH4 on the metal.

Suppressing hydrogen evolution for high selective CO2 reduction through surface-reconstructed heterojunction photocatalyst

The utilization of solar energy for CO2 reduction reaction (CO2RR) into valuable hydrocarbons offers attractive solution towards low-carbon future, but their performance is affected by the competing hydrogen evolution reaction (HER) that occurs simultaneously. Herein, we proposed maximizing interface integration and surface reconstructing engineer strategy to improve the CO2RR activity and selectivity of heterojunction photocatalyst. A surface-reconstructed ZnO/CuOx catalysts are uniformly anchored on the porous carbon nanosheet arrays that are supported by carbon nanofibers (ZnO/CuOx-C CNFs). Downsizing ZnO/CuOx maximizes the interface integration of components to promote electron-hole pairs separation and increase surface active site density. Moreover, the surface reconstruction (the formation of the hydroxyl groups on ZnO via facile light irradiation) promotes the kinetic of CO2RR to CH4 and oxygen evolution reaction (OER), while depressing the competing HER and CO generation. All these advantages contribute to the excellent catalytic performance: a high CH4 generation rate of 241.6 μmol h−1 g−1 with the selectivity of ∼96 % for ZnO/CuOx-C CNFs under full light irradiation. The insight into the modification of photocatalyst structure and mechanism investigation pave the way for a new design strategy to advance solar photocatalytic technology for CO2 reduction.

Selective hydrogenation of acetylene on Cu-Pd intermetallic compounds and Pd atoms substituted Cu(111) surfaces.

The selective hydrogenation of acetylene was studied on the ordered Cu-Pd intermetallic compounds (L10-type CuPd, L12-type Cu3Pd, and L12-type CuPd3) and Pd-modified Cu(111) surfaces through first-principles calculations. The catalytic selectivity and activity of Cu-Pd alloy catalysts are closely related to the crystal structure and composition of Cu-Pd intermetallic compounds and the size of Pd ensembles of Cu-based dilute alloy surface for the selective hydrogenation of acetylene to ethylene. Significantly, we found that the ordered Cu-Pd alloy surface containing isolated Pd atoms (i.e., L12-type Cu3Pd(111) surface) is highly efficient for the selective hydrogenation reaction of C2H2 + H2→ C2H4. The contiguous Pd atom ensembles (Pd dimer and trimer) are catalytically active towards C2H2 + H → C2H3 and C2H3 + H → C2H4 reactions than the single Pd atom on a Pd-decorated Cu(111) surface. However, the small Pd ensembles on Cu(111) present a low chemical activity for H2 dissociation compared with the ordered Cu-Pd intermetallic compounds. Our theoretical results provide a strategy of crystal phase and composition control for enhancing the selectivity and activity of Cu-Pd catalysts towards acetylene selective hydrogenation.

A neural network potential energy surface for the F + H2O ↔ HF + OH reaction and quantum dynamics study of the isotopic effect.

A global potential energy surface for the F + H2O ↔ HF + OH reaction has been constructed using the neural network method based on ∼24 000 ab initio energies calculated at the all-electron CCSD(T)-F12a/cc-pCVTZ-F12 level of theory. The correction term accounting for the influence of spin-orbit couplings has also been included with a hierarchical scheme. The isotopic effect on the total reaction probabilities of the reaction was investigated using the time-dependent wave packet method.

Time-dependent quantum dynamics study of the F + C2H6 → HF + C2H5 reaction

The cross sections of the F + C2H6 → HF + C2H5 reaction obtained using quantum dynamics calculations agree with the quasi-classical trajectory results and the full-dimensional quantum rates are in good agreement with the experimental and theoretical results.

A ten-dimensional quantum dynamics model for the X + YCAB2 reaction: Application to H + CH4 reaction.

The exact description of the prototypical X + CH4 reactions in the framework of quantum mechanics is a long-standing challenge in chemical reaction dynamics. A number of reduced-dimensional models have been developed and advanced our understanding of polyatomic chemical reactivity. Here, we propose a new ten-dimensional (10D) quantum dynamics model for the kind of X + YCAB2 reaction. The new model is an extension of our previous eight-dimensional (8D) model for the X + YCZ3 reaction. In this 10D model, AB2 holds C2v symmetry and the group CAB2 is assumed to keep Cs symmetry, which gives a better description of the rocking mode of methane than the previous 8D model. The reaction dynamics of H + CH4 → H2 + CH3 is first investigated using this model. The calculations showed that the rocking mode has a similar reaction efficiency to the umbrella mode. For the degenerate asymmetric stretching mode, the averaged efficiency is comparable to that of the symmetric stretching mode.

Kinetic modeling of dynamic changing active sites in a Mars-van Krevelen type reaction: Ethylene oxychlorination on K-doped CuCl2/Al2O3

A kinetic model was developed by taking into account the dynamic nature of the active sites in Mars–van Krevelen type catalytic reactions to predict the evolution of the reactant and product composition in the gas phase and the CuCl2 concentration in the solid catalyst. The kinetic model at the steady-state of ethylene oxychlorination was obtained by combining transient experiments of the two half-reactions in the redox cycle, namely CuCl2 reduced to CuCl by ethylene and CuCl oxidation by oxygen on the K-promoted CuCl2/γ-Al2O3 catalyst. The dynamic transitions between CuCl2 and CuCl of the active sites during the reactions are also modeled, and the contributions of two active sites, namely Cu coordination numbers of 4 and 3 in CuCl2 were distinguished and included in the kinetic model. The kinetic models describe well the transient response of the reduction and oxidation steps as well as the reaction at the steady-state at different reaction conditions. Moreover, by combining the reactor modeling through a steady-state approach, the spatial-time resolved CuCl2 profile and the C2H4 reaction rate can be well predicted in comparison with the experimental results. The approach of both transient and steady-state kinetic modeling and simulation is supposed to have general relevance for a better understanding of Mars–van Krevelen type reactions.

Visible-Light-Driven Methane Conversion with Oxygen Enabled by Atomically Precise Nickel Catalyst

It remains an extreme challenge to activate thermodynamically unfavorable, chemically inert methane molecules under mild conditions. Herein, we report a molecular-like nickel-thiolate hexameric clu...

Kinetics theoretical study of the O(3P) + C2H6 reaction on an ab initio-based global potential energy surface

Based on a recently developed analytical full-dimensional potential energy surface describing the gas-phase O(3P) + C2H6 reaction (Espinosa-Garcia et al. in Phys Chem Chem Phys 22:22,591, 2020), thermal rate constants and kinetic isotope effects (KIEs) were studied in the temperature range 200–3000 K using three different kinetics tools: variational transition-state theory with multidimensional tunnelling corrections (VTST/MT), ring polymer molecular dynamics (RPMD), and quasi-classical trajectory (QCT) calculations. Except the last method, which failed in the description at low temperatures, as was expected due to its classical nature, the other two methods present rate constants with differences between them of 3% at low temperatures and 25% at high temperatures, simulate the experimental measurements in the intermediate temperature range, 500–1000 K, and are intermediate between two reviews of experimental measurements at low and high temperatures, where the experimental evidence shows differences of a factor of about 5. This result shows that both methods capture quantum effects, such as zero-point energy, tunnelling, and recrossing effects. The kinetics of the title reaction presents a non-Arrhenius behavior, where the activation energy increases with temperature. Two KIEs were analyzed. For the H/D isotopes, the KIE decreases with temperature, from 46.55 to 1.18 in the temperature range 200–3000 K, while the 12C/13C KIE presents values close to unity. Unfortunately, no experimental information is available for comparison.

Eight-Dimensional Wave Packet Dynamics Within the Quantum Transition-State Framework: State-to-State Reactive Scattering for H2 + CH3 ⇆ H + CH4.

The present work investigates the calculation of S-matrix elements for six-atom reactions combining reduced-dimensional wave packet dynamics and the quantum transition-state framework. We employ the eight-dimensional (8D) model Hamiltonian developed by Palma and Clary [J. Chem. Phys. 2000, 112, 1859-1867] and reduce basis set sizes as well as the number of wave packets by exploiting space inversion and permutation symmetry. Mode-specific chemistry in the H2 + CH3 ⇆ H + CH4 reaction is studied with full quantum-state resolution. Results for the H + CH4 reaction are compared to full-dimensional benchmark results. Detailed state-to-state results for the H2 + CH3 reaction are presented for the first time. Although the "loss of memory" effect dominates for total energies up to 0.6 eV, more complex patterns emerge at higher energies. The agreement between the present reduced-dimensional and the accurate full-dimensional results is generally good. However, shortcomings in the reduced-dimensional model can also be noted. They are related to the description of the symmetric and asymmetric C-H stretch motion in the CH4 molecule.