Nondestructive identification of colloidal molecular sieves stabilized in water

The encapsulation of small quaternary ammonium ions in zeolite frameworks could be used as a base for investigation of the crystallization process of colloidal (nanosized) molecular sieves stabilized in water with Raman and (13)C NMR spectroscopic methods. The organic-framework interactions in colloidal microporous materials with LTA, FAU, BEA, and MFI topology have been considered; the results show that the crystallinity of nanosized particles with monomodal particle size distribution stabilized in water can be examined using the vibrational and magnetic resonance spectral features of the organic template molecules occluded in the specific pores and cages in the zeolite framework. The molecular packing effect and restricted mobility due to specific organic/framework interactions result in shifts and substantial broadening of the (13)C NMR signals, as well as in changes of the positions and the relative intensities of the Raman peaks. The spectroscopic methods are very efficient for analyzing the crystalline structures of nanosized molecular sieves stabilized in aqueous suspensions due to no restrictions related to the particle size.     

Hot-Electron Photodynamics in Silver-Containing BEA-Type Nanozeolite Studied by Femtosecond Transient Absorption Spectroscopy

Silver cations were introduced in nanosized BEA-type zeolite containing organic template by ion-exchange followed by chemical reduction towards preparation of photoactive materials (Ag⁰-BEA). The stabilization of highly dispersed Ag⁰ nanoparticles with a size of 1–2 nm in the BEA zeolite was revealed. The transient optical response of the Ag-BEA samples upon photoexcitation at 400 nm was studied by femtosecond absorption. The photodynamic of the hot electrons was found to depend on the sample preparation. The lifetime of the hot electrons in the Ag−BEA samples containing small Ag nanoparticles (1–2 nm) is significantly shortened in comparison to bear Ag nanoparticles with a size of 10 nm. While for the larger Ag nanoparticles, the energy absorbed in the conduction band is decaying by electron-phonon coupling into the metal lattice, the high surface-to-volume ratio of the small Ag nanoparticles favors the dissipation of the energy of the hot electrons from the metal nanoparticles (Ag⁰) towards the zeolitic micro-environment. This finding is encouraging for further applications of Ag-containing zeolites in photocatalysis and plasmonic chemistry.     

Methane conversion into aromatic hydrocarbons over Ag-Mo/ZSM-5 catalysts

Nonoxidative methane conversion into aromatic hydrocarbons over ZSM-5-type high-silica zeolites modified with nanosized powders of molybdenum (4.0 wt %) and silver (0.1–0.5 wt %) is reported. The acidic properties of the catalysts have been investigated by temperature-programmed ammonia desorption. The microstructure and composition of the Ag-Mo/ZSM-5 catalytic systems have been studied by high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. The doping of the Mocontaining zeolite with silver enhances its activity and stability in nonoxidative methane conversion into aromatic hydrocarbons.     

纳米沸石胶体化学性质的研究

主要考察了MFI和BEA结构纳米沸石的胶体化学性质，对与纳米组装过程直接相 关的纳米沸石的电动性质体现为ξ电势）和自聚集性质进行了研究．考察了pH值、 离子强度和硅铝比对沸石ξ电势的影响．发现纳米沸石表的变化取决于其骨架结构 和组成，而电解质浓度的增大可使沸石胶粒的ξ电势减小；州增大可使ξ电势向负 电性增方向变化．较高的ξ电势是维持沸石胶液稳定的基本条件；而过小的ξ电势 则将导致纳米沸石的聚集或沉降，在毛细作用下纳米沸石可以自组装成沸石纤维， 沸石的粒径是影响该组装的关键因素，沸石粒径越小，越容易组装成致密透明的沸 石纤维．     

Effect of zeolite pore morphology on solvent-less alkylation of benzene with 1-hexene

In an attempt to convert the carcinogenic benzene which is almost restricted for its use in gasoline, alkylation reaction with olefin 1-hexene has been conducted on various zeolites. Four zeolites having different pore topology and pore size have been applied as solid acid catalysts for effective production of alkylate in a liquid phase, solvent-less low temperature reaction. The textural properties of all the four zeolites (ZSM-5, MOR, BEA, HY) have been characterized for crystal morphology by TEM, crystal structure by XRD and FTIR, BET for surface area, N₂ sorption for porosity and TPD for acidity. Among the zeolite, BEA possessed high surface area (600.61 m²/g) and enhanced meso pores volume (0.3956 cm³/g) as compared to other zeolite samples. The performance of BEA was also observed to be superior in the liquid phase alkylation of benzene with 1-hexene in a batch reactor under autogenous pressure without using any solvent. At the optimum reaction conditions, the benzene conversion was 86.6 wt% and 3-Phenylhexane, 2-Phenylhexane yield were about 47.9 wt% and 38.7 wt% respectively on this catalyst. The BEA also exhibited longer time-on-stream and reusability performance, thus offers an attractive route for converting benzene into valuable (3-Phenylhexane, 2-Phenylhexane) alkylate product useful for the manufacturing of fine chemicals, dyestuff, detergents and scents.     

Structural and sorption characteristics of the products from zeolitization of sba-15 in the presence of tetraalkylammonium hydroxides

Micro–mesoporous materials combining the structural and sorption characteristics of a mesoporous molecular sieve (MMS) and zeolite BEA were obtained by the “dry gel conversion” method – partial zeolitization of silica MMS SBA-15 in the presence of tetraethylammonium hydroxide. The volume of the mesopores reaches 0.65 cm³/g, while that of the micropores is in the region of 0.1 cm³/g. The acidity of the obtained zeolitized materials differs from that of BEA; the total concentration of medium-strength acid centers (maximum thermal desorption of ammonia at ~315 °C) amounts to 0.15 mmol/g.     

In situ infrared molecular detection using palladium-containing zeolite films

In situ IR detection of carbon monoxide in the presence of hydrocarbons (methanol and pentane) using Pd-containing zeolite thin films is reported. The thin films are prepared by spin coating deposition of nanosized LTL and BEA type zeolites suspensions; the palladium clusters are introduced in the nanosized zeolites by ion exchange followed by γ radiolysis of the coating suspensions. The Pd-containing zeolite films with a thickness of 200 nm are exposed to a single gas (either CO or hydrocarbons) or gas mixtures in the presence of water (100 ppm), and the IR spectra are collected continuously at 25, 75, and 100 °C. The fast recognition of very low concentrations of CO (2-100 ppm) in the presence of highly concentrated vapors of methanol or pentane (400-4000 ppm) with the Pd-containing zeolite films is demonstrated. The detection of CO and hydrocarbons is instant, which is a function of the low thickness of the films, small size of the individual zeolite crystals, and regular size and high stability of the Pd clusters in the zeolite films. The heat of adsorption for all experiments is similar (15 kJ.mol(-1)), which is explained with weak interactions between the carbon monoxide and palladium clusters in the zeolite films at temperatures below 100 °C. The nanosized zeolites with homogeneously distributed Pd clusters deposited in thin films demonstrate high molecular recognition capacity toward low concentrations of carbon monoxide under real environmental conditions, i.e., in the presence of water and hydrocarbons.     

氟改性对纳米 HZSM-5 分子筛催化甲醇制丙烯的影响

 在比较了纳米和微米 HZSM-5 分子筛催化甲醇制丙烯反应性能的基础上, 对纳米 HZSM-5 分子筛进行了氟改性. 利用透射电镜、N2 吸附、X 射线衍射、氨程序升温脱附和吡啶吸附-红外光谱技术对改性前后的样品进行了表征, 并在常压、500 oC 和甲醇空速 (WHSV) 为 1.0 h–1 的反应条件下, 在连续流动固定床微型反应器上考察了其催化甲醇制丙烯的性能. 结果表明, 当氟含量<10% 时, 随氟含量的增加, 改性纳米 HZSM-5 分子筛的酸量减少, 酸强度降低, 从而使丙烯选择性和催化剂稳定性不断提高. 但过量 (15%) 氟的改性使纳米 HZSM-5 分子筛的酸量、比表面积和孔容均明显减小, 致使其稳定性反而降低. 在适量 (10%) 氟改性的纳米 HZSM-5 分子筛上, 丙烯选择性和维持甲醇完全转化的反应时间分别由原来的 30.1% 和 75 h 增加到 46.7% 和 145 h.     

ESR and optical studies of cationic silver clusters in zeolite rho

Silver cationic clusters formed in γ-irradiated AgCs-rho zeolites in hydrated and dehydrated forms have been studied by electron spin resonance (ESR) spectroscopy and diffuse reflectance spectrophotometry. It was found that tetrameric silver clusters, Ag ₄ ³⁺ in dehydrated zeolites and Ag ₄ ²⁺ in hydrated samples, are stabilized at room temperature. Tetrameric silver is trapped inside octagonal prism of zeolite framework and does not show any noticeable decay as far as samples are evacuated.     

Adsorption properties of BEA zeolites and their aluminum phosphate extrudates for purification of isomaltose

The disaccharide isomaltose is produced via an enzymatic reaction and is adsorbed to BEA zeolite. This reaction integrated adsorption can be achieved as fluidized bed as well as fixed bed. We investigated isotherms, adsorption enthalpies and sorption kinetics of BEA zeolite and extrudates with a novel aluminum phosphate sintermatrix. These extrudates contain 50% (w/w) of BEA 150 zeolites (Si/Al = 75) as primary crystals. BET-surface for extrudates is 245 m²⋅g⁻¹ and 487 m²⋅g⁻¹ for zeolite. Extrudates show a monomodal macropore structure with a maximum at 90 nm. All isotherms show a type I shape. For lower equilibrium concentrations, which occur during the enzymatic reaction, Henry’s law is applied and compared to a Langmuir model. Adsorption equilibrium constant K _i,L calculated from Langmuir for extrudates at 4 °C is 64.7 mL⋅g⁻¹ and more than twice as high as obtained from Henry’s law with K _i is 26.8 mL⋅g⁻¹. Adsorption on extrudates at 4 °C is much stronger than on zeolite crystals where the Henry coefficient K _i is 17.1 mL⋅g⁻¹. Adsorption enthalpy Δh _Ad calculated from van’t Hoff plot with the Henry equation is −44.3 kJ⋅mol⁻¹ for extrudates and −29.6 kJ⋅mol⁻¹ for zeolite crystals. Finally, the kinetics for ad- and desorption were calculated from the initial slope. The diffusion rate for ad- and desorption on extrudates were in the same range while adsorption on zeolites is three orders of magnitudes faster than desorption.     

载银sod基纳米分子筛的合成及抗菌性能

采用两步法合成了sod基系列分子筛(EMT、FAU、SOD),并通过离子交换法引入Ag⁺得到载银分子筛,通过X射线衍射(XRD)、扫描电子显微镜(SEM)证明离子交换前后分子筛骨架结构和晶粒尺寸没有发生明显变化;通过红外光谱(IR)、热重(TG)证明制得的载银分子筛具有良好的稳定性;对获得的载银分子筛进行了Ag⁺释放实验与抗菌能力测试,考察了分子筛种类和晶粒尺寸对抗菌性能的影响。结果表明具有笼状结构的FAU与EMT分子筛因可储存更多的Ag⁺而具有更好的抗菌性能,而具有超笼结构的FAU分子筛抗菌性能最优。通过对比不同晶粒尺寸载银FAU分子筛抗菌数据发现,晶粒尺寸为100 nm的载银FAU分子筛因外表面丰富的抗菌活性位点以及其内部可以储存并不断释放Ag⁺而具有最优的抗菌性能和抗菌寿命。而晶粒尺寸为10 nm的载银FAU分子筛由于晶粒尺寸较小、外比表面积大、扩散路径短,Ag⁺的释放速率最快,抗菌效率最高。     

Iodide adsorption on the surface of chemically pretreated clinoptilolite

The possibility to use the monoionic Ag⁺-form (eventually Hg⁺- and Hg²⁺- forms) of clinoptilolite of domestic origin for radioactive iodide elimination from waters has been studied. The capacity of the monoforms of clinoptilolite towards iodide exceeds many times that of the capacity of clinoptilolite in natural form. Due to the low solubility product of AgI, Hg₂I₂ and HgI₂ iodides generate precipitates on the zeolite surface. Rtg analyses of the silver form of clinoptilolite after sorption of iodide demonstrate the formation of new crystals on the zeolite surface. The influence of interfering anions on the adsorption capacity of silver clinoptilolite towards iodide was investigated, too. Kinetic curves of iodide desorption from the surface of silver and mercury clinoptilolite were compared. Simultaneously, adsorption isotherms for the systems aqueous iodide solution/Ag^–, Hg-clinoptilolite were determined.     

Analytical evaluation of BEA zeolite for the pre-concentration of polycyclic aromatic hydrocarbons and their subsequent chromatographic analysis in water samples

The analytical performance of BEA – a commercial zeolite – is evaluated for the pre-concentration of fifteen Environmental Protection Agency – polycyclic aromatic hydrocarbons and their subsequent HPLC analysis in tap and lake water samples. The pre-concentration factors obtained with BEA have led to a method with excellent analytical figures of merit. One milliliter aliquots were sufficient to obtain excellent precision of measurements at the parts-per-trillion concentration level with relative standard deviations varying from 4.1% (dibenzo[a,h]anthracene) to 13.4% (pyrene). The limits of detection were excellent as well and varied between 1.1 (anthracene) and 49.9 ng L⁻¹ (indeno[1,2,3-cd]pyrene). The recovery values of all the studied compounds meet the criterion for regulated polycyclic aromatic hydrocarbons, which mandates relative standard deviations equal or lower than 25%. The small volume of organic solvents (100 μL per sample) and amount of BEA (2 mg per sample) makes sample pre-concentration environmentally friendly and cost effective. The extraction procedure is well suited for numerous samples as the small working volume (1 mL) facilitates the implementation of simultaneous sample extraction. These are attractive features when routine monitoring of numerous samples is contemplated.     

Synthesis of nanosized silver colloids by microwave dielectric heating

Silver nanosized crystallites have been synthesized in aqueous and polyols viz., ethylene glycol and glycerol, using a microwave technique. Dispersions of colloidal silver have been prepared by the reduction of silver nitrate both in the presence and absence of stabilizer poly(vinylpyrolidone) (PVP). It was observed that PVP is capable of complexing and stabilizing Ag nanoparticles formed through the reduction of Ag⁺ ions in water and ethylene glycol. In the case of ethylene glycol, it has been shown that the use of PVP leads to particles with a high degree of stability. The colloids are stable in glycerol for months even in the absence of stabilizer.     

Gamma irradiation route to synthesis of highly re-dispersible natural polymer capped silver nanoparticles

Aqueous dispersions of highly stable, redispersible silver nanoparticles (Ag NPs) were synthesized using gamma radiolysis with gum acacia as a protecting agent. The formation of nanosized silver was confirmed by its characteristic surface plasmon absorption peak at around 405 nm in UV–vis spectra. The size of the silver nanoparticles can be tuned by controlling the radiation dose, ratio of gum acacia to silver ions and also the ionic strength of the medium. Dynamic light scattering (DLS) measurement of the as-synthesized nanoparticles indicated the size less than 3 nm at higher dose of radiation and this also corroborated the size measurement from the width of the corresponding X-ray diffraction (XRD) peak. The face centered cubic (fcc) crystallinity of the nanoparticles was evident from XRD and high resolution transmission electron microscopic (HRTEM) measurements. Fourier transform infra-red (FTIR) spectroscopic data indicate a bonding of Ag NPs with COO^? group of acacia through bridging bidentate linkage.     

The stabilization of nanodisperse silver in a sulfo cation exchanger

Silver-ion exchanger (electron ion exchanger, EI) composites with equivalent silver and hydrogen counterion contents were prepared by chemical deposition. Microscopic and X-ray data showed that silver nanoparticles and their ensembles isolated from each other and stabilized by a polymeric matrix were formed. Contact of Ag⁰-EI in the H⁺ form with solutions of silver salts caused the occurrence of two processes, ion exchange and metal recrystallization. These processes were interrelated because they involved one common particle, the silver counterion. Recrystallization proceeded by the electron-ion mechanism, but, because of matrix isolation of silver particles, electron transfer occurred inside separate structural elements (ensembles of particles) rather than over the whole composite volume. The transfer of silver ions largely occurred over ionogenic matrix centers, which substantially decreased their mobility. The low electronic conductivity of the composite and limited mobility of counterions were charge stabilization factors, which hindered recrystallization and, along with matrix stabilization, contributed to the retention of nanosized silver particles.     

纳米 ZSM-22分子筛的水热合成及在甲醇转化反应中的性能

分子筛结构的独特性和多样性使其在催化、吸附分离和离子交换等领域有着广泛应用.近年来,纳米分子筛制备和应用受到极大关注.与传统微米分子筛相比,纳米分子筛具有较小的晶粒尺寸、较大的外表面积和较高的表面活性,能显著提高其分离和催化性能.制备纳米晶体的常用方法有过量模板法、空间限定法、晶种法、离子热合成法及微反应器合成法等.目前,已合成出多种拓扑结构的纳米分子筛,包括 FAU, MFI, MEL和CHA等. ZSM-22是一种具有 TON拓扑结构的一维十元环直孔道分子筛(孔口尺寸为0.45 nm ×0.55 nm),在长链烷烃异构化和烯烃异构化等反应中表现出优异的催化活性.水热合成法是制备 ZSM-22分子筛最常用的方法,所得样品晶粒尺寸为2–15μm,但由于 ZSM-22分子筛是一种亚稳态结构,为了防止杂晶生成,合成通常是在剧烈搅拌(通常大于400 r/min)下进行.目前已有报道在较低转速下合成 ZSM-22分子筛,但产物仍为微米晶体;或在微波辅助水热合成条件下合成亚微米 ZSM-22分子筛,但晶体尺寸不可调且合成过程需要较高功率的微波反应器.因此,在水热条件下合成纯纳米 ZSM-22分子筛仍然是一个巨大挑战.本文在上述研究基础上采用改进的水热合成法成功合成出纳米 ZSM-22分子筛,考察了转速﹑硅铝比及乙醇共溶剂对晶粒尺寸的影响,比较了纳米和常规微米 ZSM-22分子筛的甲醇转化反应性能.结果表明,采用改进的水热合成法能够在较低转速下合成出纳米 ZSM-22分子筛,晶体尺寸在150–800 nm范围可调.通过考察转速对晶粒尺寸的影响,发现静态合成条件下无法形成 ZSM-22分子筛,表明 ZSM-22分子筛合成需要一定的转速.转速在10–50 r/min变化时,可以合成出不同晶体尺寸的 ZSM-22分子筛,且随转速提高, ZSM-22分子筛晶体尺寸先减小后增大,表明纳米 ZSM-22分子筛合成存在最佳转速.另外,配料硅铝比能显著影响 ZSM-22分子筛晶体尺寸,随配料硅铝比增加, ZSM-22分子筛晶体尺寸先减小后增大.通过在合成体系中添加乙醇作为共溶剂,考察了有机溶剂对 ZSM-22分子筛晶粒尺寸的影响,发现有机溶剂能显著增大 ZSM-22的晶体尺寸.将本文合成的纳米和常规微米 ZSM-22分子筛用于甲醇转化反应,考察了晶体尺寸对 ZSM-22分子筛甲醇转化反应性能的影响.发现与常规微米 ZSM-22分子筛相比,纳米 ZSM-22分子筛催化剂寿命显著提高,说明晶粒尺寸减小能有效减缓积碳导致的分子筛失活;同时,反应产物中乙烯和芳烃选择性有所提高,这是由于外表面积增大所致.此外,还考察了不同硅铝比 ZSM-22分子筛的甲醇转化反应性能.结果表明,分子筛硅铝比会影响催化剂寿命,但晶体尺寸对催化剂寿命影响更大. ZSM-22分子筛硅铝比增大有助于提高低碳烯烃选择性,减少芳烃生成.     

Zeolite ZSM-5 containing copper ions: The effect of the copper salt anion and NH<Subscript>4</Subscript>OH/Cu<Superscript>2+</Superscript> ratio on the state of the copper ions and on the reactivity of the zeolite in DeNO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Isotherms of copper cation sorption by H-ZSM-5 zeolite from aqueous and aqueous ammonia solutions of copper acetate, chloride, nitrate, and sulfate are considered in terms of Langmuir’s monomolecular adsorption model. Using UV-Vis diffuse reflectance spectroscopy, IR spectroscopy, and temperatureprogrammed reduction with hydrogen and carbon monoxide, it has been demonstrated that the electronic state of the copper ions is determined by the ion exchange and heat treatment conditions. The state of the copper ions has an effect on the redox properties and reactivity of the Cu-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO with propane and in N₂O decomposition. The amount of Cu²⁺ that is sorbed by zeolite H-ZSM-5 from aqueous solution and is stabilized as isolated Cu²⁺ cations in cationexchange sites of the zeolite depends largely on the copper salt anion. The quantity of Cu(II) cations sorbed from aqueous solutions of copper salts of strong acids is smaller than the quantity of the same cations sorbed from the copper acetate solution. When copper chloride or sulfate is used, the zeolite is modified by the chloride or sulfate anion. Because of the presence of these anions, the redox properties and nitrogen oxides removal (DeNO _x ) efficiency of the Cu-ZSM-5 catalysts prepared using the copper salts of strong acids are worse than the same characteristics of the sample prepared using the copper acetate solution. The addition of ammonia to the aqueous solutions of copper salts diminishes the copper salt anion effect on the amount of Cu(II) sorbed from these solutions and hampers the nonspecific sorption of anions on the zeolite surface. As a consequence, the redox and DeNO _x properties of Cu-ZSM-5 depend considerably on the NH₄OH/Cu²⁺ ratio in the solution used in ion exchange. The aqueous ammonia solutions of the copper salts with NH₄OH/Cu²⁺ = 6–10 stabilize, in the Cu-ZSM-5 structure, Cu²⁺ ions bonded with extraframework oxygen, which are more active in DeNO _x than isolated Cu²⁺ ions (which form at NH4OH/Cu2+ = 30) or nanosized CuO particles (which form at NH₄OH/Cu²⁺ = 3).     

纳米薄层HZSM-5分子筛催化甲醇制丙烯

在合成系列硅铝比纳米薄层HZSM-5分子筛的基础上,研究了纳米薄层HZSM-5分子筛催化甲醇制丙烯(MTP)的反应性能.在固定床微反装置上详细考察了工艺条件对纳米薄层HZSM-5分子筛催化性能的影响,同时与纳米HZSM-5分子筛对MTP反应的催化性能进行了比较.结果表明,纳米薄层HZSM-5分子筛具有较高的目的产物选择性和较长的催化寿命.在适宜硅铝比(n(SiO2)/n(Al2O3)=213)和反应条件下(温度470°C,甲醇质量空速为3 h-1),丙烯的选择性达到46.7%,三烯(乙烯、丙烯和C4烯烃)选择性达到78.7%.其中,丙烯/乙烯的质量比可达到6.5,是纳米HZSM-5分子筛的2倍,而芳烃的选择性比纳米分子筛明显降低.这是因为纳米薄层HZSM-5分子筛比纳米HZSM-5分子筛具有较宽的(010)晶面、较大的外比表面积和介孔孔容.     

Synthesis of Pure Silica MWW Zeolite in Fluoride Medium by Using an Imidazolium-Based Long Dication

As the spacer length in 1,2-dimethylimidazolium-based dications increases beyond a specific point (six methylene units), they fail in structure-directing towards STW zeolites in any synthetic conditions. These dications can instead produce, under fluoride concentrated conditions, either *BEA [in the case of the eight-methylene-unit structure-directing agent (SDA)] or MWW (ten methylene units) zeolites. For any length of the dication, the default zeolite (MTW) is a relatively dense zeolite containing a unidimensional channel, whereas the zeolite demanding most specificity (STW, *BEA or MWW) is more porous, affording a larger concentration of the dication to be occluded. This work provides the first reported fluoride synthesis of pure silica MWW zeolites. Charge balance of the organic dications in this zeolite was achieved by combining “structural” silanolates, regular “connectivity defects” and occluded fluoride. Molecular mechanics calculations showed a perfect fit of the decamethylenebis(dimethylimidazolium) dication in the sinusoidal intralayer pore system of MWW. The calculations showed also that the dication is able to stabilize the interlayer space without disturbing the hydrogen-bonding system that holds the layers together in the as-made material. The ¹⁹F magic-angle spinning (MAS) NMR presented two distinct resonances at −71 and −83 ppm, which, on the basis of DFT calculations, we tentatively assigned to fluoride occluded in [4⁶6²] and [4¹5²6²] cages of the MWW structure, respectively. The same DFT study determines a different chemical shift of one methyl ¹³C nuclear magnetic resonance according to the imidazolium ring residing in the sinusoidal channels or in the large cup cavities, thus explaining an experimentally observed splitting of that resonance.