Torr Of He Research Articles

Synthesis, Characterization of Nanostructured Rhodium Films and their Electrochemical Behavior towards Carbon Monoxide Oxidation

Rhodium nanostructured thin film catalysts were prepared by pulsed laser deposition. The depositions were performed under vacuum and at different He background gas pressures ranging from 1 to 5 Torr. SEM, TEM, X-ray diffraction, and X-ray photoelectron spectroscopy were used to evaluate the morphology, the structure, the surface composition, and the electronic structure of the catalysts. Their electrochemical properties were studied towards CO stripping measurements in acidic solution; a reaction of critical issue to liquid fuel cells. It was discovered that rhodium (Rh) film deposited under 5 Torr of He background pressure showed the highest electroactive surface area, and the lowest onset potential of CO oxidation demonstrating an enhancement of the CO poisoning resistance. The reason for such enhanced electrocatalytic activity is ascribed to the high porosity and roughness of the Rh surface. Compared to Pt films made under similar processing conditions (5 Torr of He), Rh film displayed higher roughness factor of 58.5 (vs. 30 for Pt), a net charge due to oxidation and desorption of the CO adlayer of 385 μC cm−2 (vs. 350 μC cm−2 for Pt), and an onset potential for CO oxidation of 30 mV less anodic than that at Pt electrode.

Tropospheric photooxidation of CF<sub>3</sub>CH<sub>2</sub>CHO and CF<sub>3</sub>(CH<sub>2</sub>)<sub>2</sub>CHO initiated by Cl atoms and OH radicals

Abstract. The absolute rate coefficients for the tropospheric reactions of chlorine (Cl) atoms and hydroxyl (OH) radicals with CF3CH2CHO and CF3(CH2)2CHO were measured as a function of temperature (263–371 K) and pressure (50–215 Torr of He) by pulsed UV laser photolysis techniques. Vacuum UV resonance fluorescence was employed to detect and monitor the time evolution of Cl atoms. Laser induced fluorescence was used in this work for the detection of OH radicals as a function of reaction time. No pressure dependence of the bimolecular rate coefficients, kCl and kOH, was found at all temperatures. At room temperature kCl and kOH were (in 10−11 cm3 molecule−1 s−1): kCl(CF3CH2CHO) = (1.55±0.53); kCl(CF3(CH2)2CHO) = (3.39±1.38); kCl(CF3CH2CHO) = (0.259±0.050); kCl(CF3(CH2)2CHO) = (1.28±0.24). A slightly positive temperature dependence of kCl was observed for CF3CH2CHO and CF3(CH2)2CHO, and kOH(CF3CH2CHO). In contrast, kOH(CF3(CH2)2CHO) did not exhibit a temperature dependence over the range investigated. Arrhenius expressions for these reactions were: kCl(CF3CH2CHO) = (4.4±1.0)×10−11 exp{−(316±68)/T} cm3 molecule−1 s−1 kCl(CF3(CH2)2CHO) = (2.9±0.7)×10−10 exp{−(625±80)/T} cm3 molecule−1 s−1 kOH(CF3CH2CHO) = (7.8±2.2)×10−12 exp{−(314±90)/T} cm3 molecule−1 s−1 The atmospheric impact of the homogeneous removal by OH radicals and Cl atoms of these fluorinated aldehydes is discussed in terms of the global atmospheric lifetimes, taking into account different degradation pathways. The calculated lifetimes show that atmospheric oxidation of CF3(CH2)x CHO are globally dominated by OH radicals, however reactions initiated by Cl atoms can act as a source of free radicals at dawn in the troposphere.

Kinetic study of the reaction of chlorine atoms with 3-methyl-3-buten-1-ol

The reaction of a typical unsaturated alcohol, 3-methyl-3-buten-1-ol (MBO331), with Cl atoms, was investigated for the first time. The reaction was investigated using discharged flow-tube coupled with electron impact mass spectrometer. The experiments were performed over the temperature range of 248 K-298 K and at pressure of 1 torr in He as the bath gas. The obtained kinetic data were used to derive the Arrhenius expression: k 1 = (3.47 ± 1.21) × 10−11 exp[(599 ± 69)/T] cm3 molecule−1 s−1. Finally, atmospheric lifetimes of the MBO331 with respect to OH radicals, NO3 radicals and Cl atoms have been calculated and the atmospheric implications are considered briefly.

M2@C79N (M = Y, Tb): isolation and characterization of stable endohedral metallofullerenes exhibiting M-M bonding interactions inside aza[80]fullerene cages.

Y2@C79N and Tb2@C79N have been prepared by conducting the Kratschmer-Huffman electric-arc process under 20 Torr of N2 and 280 Torr of He with metal oxide-doped graphite rods. These new heterofullerenes were separated from the resulting mixture of empty cage fullerenes and endohedral fullerenes by chemical separation and a two-stage chromatographic process. Crystallographic data for Tb2@C79N x Ni(OEP) x 2 C6H6 demonstrate the presence of an 80-atom cage with idealized I(h) symmetry and two, widely separated Tb atoms inside with a Tb-Tb separation of 3.9020(10) A for the major terbium sites. The EPR spectrum of the odd-electron Y2@C79N indicates that the spin density largely resides on the two equivalent yttrium ions. Computational studies on Y2@C79N suggest that the nitrogen atom resides at a 665 ring junction in the equator on the fullerene cage and that the unpaired electron is localized in a bonding orbital between the two yttrium ions of this stable radical. Thus, the Tb-Tb bond length of the single-electron bond is an exceedingly long metal-metal bond.

Dendrimer Templated Synthesis of One Nanometer Rh and Pt Particles Supported on Mesoporous Silica: Catalytic Activity for Ethylene and Pyrrole Hydrogenation

Monodisperse rhodium (Rh) and platinum (Pt) nanoparticles as small as approximately 1 nm were synthesized within a fourth generation polyaminoamide (PAMAM) dendrimer, a hyperbranched polymer, in aqueous solution and immobilized by depositing onto a high-surface-area SBA-15 mesoporous support. X-ray photoelectron spectroscopy indicated that the as-synthesized Rh and Pt nanoparticles were mostly oxidized. Catalytic activity of the SBA-15 supported Rh and Pt nanoparticles was studied with ethylene hydrogenation at 273 and 293 K in 10 torr of ethylene and 100 torr of H 2 after reduction (76 torr of H 2 mixed with 690 torr of He) at different temperatures. Catalysts were active without removing the dendrimer capping but reached their highest activity after hydrogen reduction at a moderate temperature (423 K). When treated at a higher temperature (473, 573, and 673 K) in hydrogen, catalytic activity decreased. By using the same treatment that led to maximum ethylene hydrogenation activity, catalytic activity was also evaluated for pyrrole hydrogenation.

Atmospheric Degradation of 2-Butanol, 2-Methyl-2-butanol, and 2,3-Dimethyl-2-butanol: OH Kinetics and UV Absorption Cross Sections

The absolute rate coefficients for the reactions of hydroxyl radical (OH) with 2-butanol (k(1)), 2-methyl-2-butanol (k(2)), and 2,3-dimethyl-2-butanol (k(3)) were measured as a function of temperature (263-354 K) and pressure (41-193 Torr of He, Ar, and N(2)) by the pulsed laser photolysis/laser-induced fluorescence technique. This work represents the first absolute determination of k(1)(-)k(3) and their temperature dependence. No pressure dependence of the rate coefficients was observed in the range studied. Thus, k(i)(298 K) values (x10(-12) cm(3) molecule(-1) s(-1) with an uncertainty of +/-2sigma) were averaged over the pressure range studied yielding 8.77 +/- 1.46, 3.64 +/- 0.60, and 9.01 +/- 1.00 for 2-butanol (k(1)), 2-methyl-2-butanol (k(2)), and 2,3-dimethyl-2-butanol (k(3)), respectively. k(1) and k(3) exhibit a slightly negative temperature dependence over the temperature range studied. In contrast, the rate coefficient for the reaction of OH with 2-methyl-2-butanol (k(2)) did not show any temperature dependence. Some deviation of the conventional Arrhenius behavior was clearly observed for k(3). In this case, the best fit to our data was found to be described by the three-parameter expression k(T) = A + B exp(-C/T). The UV absorption cross sections of 2-butanol, 2-methyl-2-butanol, and 2,3-dimethyl-2-butanol have also been measured at room temperature between 208 and 230 nm. The values reported constitute the first determination of the UV cross sections of those alcohols. Our results are compared with previous studies, when possible, and are discussed in terms of the H-abstraction by OH radicals. The atmospheric implications of these reactions and the photochemistry of these alcohols are also discussed.

Laser and Fourier transform emission spectroscopy of TaCl

The emission spectrum of TaCl has been recorded at high resolution in the 3000–35 000 cm −1 region using a Fourier transform spectrometer. The bands were observed by microwave excitation of a mixture of TaCl 5 vapor and 3.0 Torr of He. Several TaCl bands have also been recorded using the laser ablation/molecular beam source at the University of New Brunswick. A rotational analysis of a number of bands has been obtained and the majority of the stronger bands have been classified into three groups with different lower state spectroscopic constants. The three lower states have been identified as having Ω″ = 0 +, Ω″ = 2, and (tentatively) Ω″ = 3. The Ω″ = 0 + and Ω″ = 2 states are very close in energy and one of these two states is the ground state of TaCl.

Fourier transform emission spectroscopy of the F4Δ– X4Φ system of TiF

The emission spectra of TiF have been reinvestigated in the 4200–15 000 cm −1 region using the Fourier transform spectrometer associated with the National Solar Observatory at Kitt Peak. TiF was formed in a microwave discharge lamp operated with 2.5 Torr of He and a trace of TiF 4 vapor, and the spectra were recorded at a resolution of 0.02 cm −1. The TiF bands observed in the 12 000–14 000 cm −1 region have been assigned to a new transition, F 4Δ– X 4Φ. Each band consists of four sub-bands assigned as, 4Δ 1/2– 4Φ 3/2, 4Δ 3/2– 4Φ 5/2, 4Δ 5/2– 4Φ 7/2, and 4Δ 7/2– 4Φ 9/2. A rotational analysis of the 0–1, 0–0, and 1–0 bands has been obtained and spectroscopic constants have been extracted.

248-nm Laser Photolysis of CHBr3/O-Atom Mixtures: Kinetic Evidence for UV CO(A) Chemiluminescence in the Reaction of Methylidyne Radicals with Atomic Oxygen

The 4th positive and Cameron band emissions from electronically excited CO have been observed for the first time in 248-nm pulsed laser photolysis of a trace amount of CHBr(3) vapor in an excess of O atoms. O atoms were produced by dissociation of N(2)O (or O(2)) in a cw-microwave discharge cavity in 2.0 Torr of He at 298 K. The CO emission intensity in these bands showed a quadratic dependence on the laser fluence employed. Temporal profiles of the CO(A) and other excited-state products that formed in the photoproduced precursor + O-atom reactions were measured by recording their time-resolved chemiluminescence in discrete vibronic bands. The CO 4th positive transition (A(1)Pi, v' = 0 --> X(1)Sigma(+), v' ' = 2) near 165.7 nm was monitored in this work to deduce the pseudo-first-order decay kinetics of the CO(A) chemiluminescence in the presence of various added substrates (CH(4), NO, N(2)O, H(2), and O(2)). From this, the second-order rate coefficient values were determined for reactions of these substrates with the photoproduced precursors. The measured reactivity trends suggest that the prominent precursors responsible for the CO(A) chemiluminescence are the methylidyne radicals, CH(X(2)Pi) and CH(a(4)Sigma(-)), whose production requires the absorption of at least 2 laser photons by the photolysis mixture. The O-atom reactions with brominated precursors (CBr, CHBr, and CBr(2)), which also form in the photolysis, are shown to play a minor role in the production of the CO(A or a) chemiluminescence. However, the CBr(2) + O-atom reaction was identified as a significant source for the 289.9-nm Br(2) chemiluminescence that was also observed in this work. The 282.2-nm OH and the 336.2-nm NH chemiluminescences were also monitored to deduce the kinetics of CH(X(2)Pi) and CH(a(4)Sigma(-)) reactions when excess O(2) and NO were present.

Theoretical and Experimental Study of the Product Branching in the Reaction of Acetic Acid with OH Radicals

The product distribution of the reaction of acetic acid, CH(3)COOH, with hydroxyl radicals, OH, was studied experimentally and theoretically. Mass-spectrometric measurements at 290 K and 2 Torr of He of the CO(2) yield versus the loss of acetic acid yielded a branching fraction of 64 +/- 14% for the abstraction of the acidic hydrogen as follows: CH(3)COOH + OH --> CH(3)COO + H(2)O --> CH(3) + CO(2) + H(2)O. A quantum chemical and theoretical kinetic analysis showed that the abstraction of the acidic hydrogen is enhanced relative to the abstraction of -CH(3) hydrogens because of the formation of a strong pre-reactive H-bonded complex, where the H-bonds are retained in the H-abstraction transition state. The potential energy surface of the reaction is explored in detail, and the reaction products of the individual channels are identified. The theoretical product branching is found to be critically dependent on the energetic and rovibrational differences between the H-abstraction transition states.

Kinetic and mechanistic studies of the recombination of OH with NO2: Vibrational deactivation, isotopic scrambling and product isomer branching ratios

The kinetics and mechanism of the three-body recombination of OH with NO2 were studied using a pulsed laser photolysis pulsed laser induced fluorescence technique. The rate coefficients for deactivation of vibrationally excited OH (v = 1-5) by NO2 were found to be independent of vibrational level with a value of (6.4 +/- 0.3) x 10(-11) cm3 molecule s (-1) at 298 K. The rate coefficient for reaction of 18OH with NO2 was measured and found to be much faster than for unlabeled OH with a "zero pressure" rate of 1 x 10(-11) cm3 molecule(-1) s(-1) at 298 K and 273 K. Observation of temporal profiles of 16OH and 18OH suggest that isotopic scrambling in the initially formed [H18ON16O2] complex is complete on the microsecond time scale of our experiments. The rate coefficient for reaction of unlabeled OH with NO2 was measured at 413 K in 400 Torr of He. Biexponential temporal profiles were obtained and are consistent with a 10 +/- 3% yield of the weakly bound HOONO isomer.

Tropospheric Reaction of OH with Selected Linear Ketones: Kinetic Studies between 228 and 405 K

The absolute rate coefficients for the tropospheric reactions of hydroxyl radical (OH) with a series of linear aliphatic ketones (2-butanone (k1), 2-pentanone (k2), 2-hexanone (k3), and 2-heptanone (k4)) were measured as a function of temperature (228-405 K) and pressure (45-600 Torr of He) by the pulsed laser photolysis/laser induced fluorescence technique. These studies are essential to model the atmospheric chemistry of these ketones and their impact in the air quality. No pressure dependence of the rate coefficients was observed in the range studied. Thus, k1(298 K) (x10(-12) cm3 molecule(-1) s(-1)) were averaged over the pressure range studied yielding the following: (1.04+/-0.74), (3.14+/-0.40), (6.37+/-1.40), and (8.22+/-1.10), for 2-butanone (k1), 2-pentanone (k2), 2-hexanone (k3), and 2-heptanone (k4), respectively. k1 exhibits a slightly positive temperature dependence over the temperature range studied. A conventional Arrhenius expression describes the observed behavior. In contrast, the temperature dependence of k2-k4 shows a distinct deviation from the Arrhenius behavior. The best fit to our data was found to be described by the three-parameter expression: k(T) = A + B exp(-C/T) in cm3 molecule(-1) s(-1). This work constitutes the first determination of the temperature dependence of k2-k4. Our results are compared with previous studies, when possible, and are discussed in terms of the H-abstraction by OH radicals. The atmospheric implications of these reactions are also discussed.

Infrared emission spectroscopy of a new 2Σ– 2Σ system of TiCl

The spectra of TiCl have been reinvestigated in the 4200–8500 cm −1 region using the 1-m Fourier transform spectrometer associated with the National Solar Observatory at Kitt Peak. The molecules were excited in a microwave discharge lamp operated with 3.0 Torr of He and a trace of TiCl 4 vapor, and the spectra were recorded at a resolution of 0.01 cm −1. Three new bands with origins near 6938.9, 6900.2, and 6861.7 cm −1 have been assigned as the 0–0, 1–1, and 2–2 bands of a new 2 Σ – 2 Σ transition. This assignment is supported by our recent ab initio calculations on TiCl and ZrCl [J. Chem. Phys. 114 (2001) 3977]. A rotational analysis of these bands has been carried out and spectroscopic constants have been extracted for the 2 Σ states.

Cool pulsed molecular microbeam

We produce a cool pulsed supersonic molecular beam of CaF radicals essentially without recourse to pumping. The radicals are generated by laser ablating a solid precursor target in a small ablation cell of volume of about 0.01 cm3. The target is ablated through a 750 μm orifice by a pulsed Nd:YAG laser. The ablation plume supersonically expands into a vacuum chamber and cools the initially hot CaF molecules seeded in it. We enhance the supersonic character of the expansion by feeding into the ablation cell about 10 Torr of He, Ar, or Xe carrier gas. The CaF molecules are probed by time-dependent laser absorption spectroscopy. With a Xe carrier, about 1012 CaF molecules are found to be seeded in a single pulse and cooled down to a terminal translational temperature of about 140 K. We expect that a wide variety of species, including highly unstable ones, will be amenable to forming such a cool intense molecular microbeam, to the benefit of spectroscopy, reaction dynamics, and microfabrication.

Fourier transform emission spectroscopy of the [formula omitted]– [formula omitted] system of FeCl

The emission spectrum of FeCl has been investigated at high resolution in the near infrared. The molecule was excited in a microwave discharge lamp using a mixture of FeCl 3 vapor and 4.9 Torr of He, and the spectra were recorded in the 3000–12 200 cm −1 region using a Fourier transform spectrometer. New bands with R heads near 7725, 8149, 8577, 8949, 9319, 9686, and 10 050 cm −1 have been assigned as the 0–2, 0–1, 0–0, 1–0, 2–0, 3–0, and 4–0 bands (respectively) of a new 4Δ– 4Δ system of FeCl. The strong bands of this system consist of four sub-bands assigned as 4Δ 1/2– 4Δ 1/2, 4Δ 3/2– 4Δ 3/2, 4Δ 5/2– 4Δ 5/2, and 4Δ 7/2– 4Δ 7/2. This transition is analogous to the 1 μm transitions of FeH and FeF. A rotational analysis of a number of bands in each sub-band has been obtained and spectroscopic constants extracted. The lower a 4 Δ state is affected by perturbations from a nearby electronic state, while the excited g 4Δ state is free from perturbation. This work represents the first observation of a transition involving quartet states of FeCl.

Kinetics and Mechanism of the O Atom Reaction with Dimethyl Sulfoxide

The kinetics and mechanism of the reaction O + DMSO → products (1) have been studied by the mass spectrometric discharge-flow method at 298 K and at a total pressure of 1 Torr of helium. The reaction rate coefficient was measured under pseudo-first-order conditions either from the kinetics of O atom consumption in excess of DMSO or from the kinetics of DMSO decay in excess of O atoms: k1 = (1.0 ± 0.2) × 10-11 cm3molecule-1s-1 (uncertainty includes 2σ statistical error and estimated systematic errors). Both CH3 and SO2 were detected as the products of reaction 1, and the reaction O + DMSO → 2CH3 +SO2 was found to be the main (if not unique) channel of reaction 1 under the experimental conditions of the study. This result indicates that reaction 1 cannot be a suitable laboratory source of the atmospheric relevant CH3SO2 radical, at least at low pressures. In addition, the upper limits, k3 < 1 × 10-13 and k4 < 5 × 10-15 cm3 molecule-1 s-1, were determined for the rate coefficients of the reactions CH3 + DMSO → products (3) and Br2 + DMSO → products (4), respectively. The rate constant of the self-combination of CH3 radicals, CH3 + CH3 (+M) → C2H6 (+M) (2), was also determined in the pressure range between 0.5 and 3.0 Torr of He.

Collision-Free Lifetimes of SO(B3Σ-, v‘ = 0, 1, and 2) and Vibrational Level Dependence of Deactivation by He

Collision-free lifetimes and deactivation rate constants of SO(B3Σ-, v‘ = 0, 1, and 2) by collisions with He have been determined. SO(X3Σ-) was generated in the photolysis of SO2 at 193 nm (ArF laser) and excited to a single rovibrational level of B3Σ- with a pulsed ultraviolet laser. We recorded dispersed fluorescence spectra, and found that 0−12 (350.8 nm), 1−14 (368.5 nm), and 2−17 (401.2 nm) bands are suitable for detecting fluorescence from single vibrational level of interest. Time profiles of wavelength-resolved fluorescence were recorded at various buffer gas pressures (5−165 Torr of He). Deconvolution by the integrated phase plane method derives apparent fluorescence lifetime at a given pressure. Total pressure dependence of fluorescence decay rates leads to collision-free lifetimes and rate constants for deactivation of SO(B3Σ-, v‘ = 0, 1, and 2) by collisions with He. Lifetimes of SO(B3Σ-) have been determined to be (28 ± 2) ns (v‘ = 0), (30 ± 3) ns (v‘ = 1), and (27 ± 4) ns (v‘ = 2). Rate coef...

Kinetics of the OH + Methyl Vinyl Ketone and OH + Methacrolein Reactions at Low Pressure

The rate constants for the OH + methyl vinyl ketone and OH + methacrolein reactions have been measured in 2−5 Torr of He and over the temperature range 300−422 K using discharge-flow systems coupled with laser-induced fluorescence and resonance fluorescence detection of the OH radical. The rate constant for the OH + methyl vinyl ketone reaction was found to be (1.73 ± 0.21) × 10-11 cm3 molecule-1 s-1 at 5 Torr. No significant pressure dependence was observed between 2 and 5 Torr at 300 K, but a pressure dependence of the rate constant was measured at temperatures between 328 and 422 K. At 328 K, the termolecular rate constant (k0) was measured to be (6.71 ± 2.65) × 10-28 cm6 molecule-2 s-1. An Arrhenius expression of k0 = (9.9 ± 7.6) × 10-30 exp[(1440 ± 300)/T] cm6 molecule-2 s-1 over the temperature range 328−422 K was obtained from a weighted linear least-squares fit of the k0 data versus temperature. Unlike the OH + methyl vinyl ketone reaction, a significant pressure dependence of the rate constant fo...

CH3O Yield in the CH3+ O3Reaction Using the LP/LIF Technique at Room Temperature

CH3O(X2E) radicals have been detected by laser-induced fluorescence (LIF) for the first time as a product of the reaction between CH3 and O3. CH3 radicals were generated by excimer-laser photolysis of CH3Br at 193 nm in the presence of O3 at room temperature and 100 Torr of He. The rate constant for reaction 1a (CH3 + O3 → CH3O + O2) has been determined by monitoring the CH3O build-up as a function of reaction time and k1a was found to be (9.68 ± 1.10) × 10-14 cm3 molecule-1 s-1. The rate coefficient of the global reaction 1 (CH3 + O3 → products) has been determined by the numerical analysis of the CH3O temporal profiles, yielding a value of k1 = (2.2 ± 0.3) × 10-12 cm3 molecule-1 s-1. Reaction of CH3 with NO2 has also been studied under the same experimental conditions as reaction 1 and has been used to calibrate the CH3O LIF signal. On the other hand, the rate constant k2 for reaction 2 (CH3O + O3 → products) has been directly determined (k2(T = 298 K) = (2.53 ± 0.75) × 10-14 cm3 molecule-1 s-1) using t...

Measurements of the kinetics of the OH + α‐pinene and OH + β‐pinene reactions at low pressure

AbstractThe rate constants for the OH + α‐pinene and OH + β‐pinene reactions have been measured in 5 Torr of He using discharge‐flow systems coupled with resonance fluorescence and laser‐induced fluorescence detection of the OH radical. At room temperature, the measured effective bimolecular rate constant for the OH + α‐pinene reaction was (6.08 ± 0.24) × 10−11 cm3 molecule−1 s−1. These results are in excellent agreement with previous absolute measurements of this rate constant, but are approximately 13% greater than the value currently recommended for atmospheric modeling. The measured effective bimolecular rate constant for the OH + β‐pinene reaction at room temperature was (7.72 ± 0.44) × 10−11 cm3 molecule−1 s−1, in excellent agreement with previous measurements and current recommendations. Above 300 K, the effective bimolecular rate constants for these reactions display a negative temperature dependence suggesting that OH addition dominates the reaction mechanisms under these conditions. This negative temperature dependence is larger than that observed at higher pressures. The measured rate constants for the OH + α‐pinene and OH + β‐pinene reactions are in good agreement with established reactivity trends relating the rate constant for OH + alkene reactions with the ionization potential of the alkene when ab initio calculated energies for the highest occupied molecular orbital are used as surrogates for the ionization potentials for α‐ and β‐pinene. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 300–308, 2002