Ultraviolet photodissociation of iodine monochloride (ICl) at 235, 250, and 265 nm

ICl photolysis in the ultraviolet region of the spectrum (235-265 nm) is studied using the Slice Imaging technique. The Cl?((2)P(1/2))/Cl((2)P(3/2)) and the I?((2)P(1/2))/I((2)P(3/2)) branching ratio between the I((2)P(3/2)) + Cl((2)P(3/2))∕Cl?((2)P(1/2)) and I?((2)P(1/2)) + Cl((2)P(3∕/2))∕Cl?((2)P(1/2)) channels is extracted from the respective iodine and chlorine photofragment images. We find that ground state chlorine atoms (Cl((2)P(3/2))) are formed nearly exclusively with excited state iodine atoms (I?((2)P(1/2))), while excited spin-orbit chlorine atoms (Cl?((2)P(1/2))) are concurrently produced only with ground state iodine atoms (I((2)P(3/2))). We conclude that photolysis of ICl in this UV region is a relatively "clean" source of spin-orbit excited chlorine atoms that can be used in crossed molecular beam experiments.     

F~2, F与I~2的化学发光反应

在流动余辉实验装置上,研究了F~2,F与I~2的化学发光反应。首次在F+I~2反应体系中观察到较强的IF(B→X)发射光谱,采用简单碰撞理论对IF(B)的振动驰豫进行估算后,得到了其振动布居,发现与F~2+I~2反应体系有明显的不同,从而推测这两个反应的激发态产物IF(B)是由不同的反应通道形成的。前者由初级反应产物I~2F与F原子进一步作用产生,而后者则由激发态的I(^2p~1~/~2)与基态的F(^2p~3~/~2)碰撞复合产生。     

A denuder-impinger system with in situ derivatization followed by gas chromatography-mass spectrometry for the determination of gaseous iodine-containing halogen species

Reactive iodine species have been suggested to play an important role in the atmosphere (e.g. tropospheric ozone depletion, coastal new particle formation). However, there still exist major uncertainties about their atmospheric chemistry, mostly due to the lack of analytical approaches for the accurate speciation of certain key compounds. In this study, 1,3,5-trimethoxybenzene (1,3,5-TMB)-coated denuder proved to be suitable for the differentiation between gaseous interhalogens (iodine monochloride (ICl), iodine monobromide (IBr)) and molecular iodine (I2) based on a selective collection/derivatization method. The results of the denuder sampling were compared with the results of impinger sampling in water, methanol and carbon tetrachloride solutions of 1,3,5-TMB. ICl and IBr are converted into 1-iodo-2,4,6-trimethoxybenzene (1-iodo-2,4,6-TMB) and 1-bromo-2,4,6-trimethoxybenzene (1-bromo-2,4,6-TMB), respectively, in the denuder systems. The respective collection efficiency is 99.2% for ICl and 92.6% for IBr, at 500mLmin(-1) gas flow rate. The collection efficiency for I2 is lower than 1% in the same denuder system, but significantly increases to about 90% in the aqueous 1,3,5-TMB loaded impinger. The denuder-impinger coupled system was then used to differentiate and to collect the ICl, IBr and I2 gas mixtures, followed by gas chromatography-ion trap mass spectrometry (GC-MS) determination. The precision of the method is in general better than 9.1%. The parameters affecting denuder operation including sampling flow rate, sampling duration, and relative humidity have been evaluated. The presented method provides an attractive protocol for iodine species analysis for atmospheric chemistry research.     

Evidence for the reaction of a long-lived monotypic species of iodine in the gas phase

A monotypic long-lived radioactive iodine of¹²³I or¹²⁵I resulting from the¹²³I or¹²⁵Xe(EC)¹²⁵I nuclear transformation, respectively, is described. The iodine species has the characteristics thought peculiar to the hydrated halogen that participates in certain concerted termolecular halogen-halogen reactions. The reaction leading to¹²³ICl or¹²⁵ICl in gas phase substrates of Cl₂, NOCl, HCl and CCl₄ was studied. Deceased, visiting scientist during 1972 from the Institute of Atomic Physics, Bucharest. Romania.     

Exploring the chemistry of free CI3+: reactions with the weak Lewis bases PX3 (X = Cl-I), AsI3 and Et2O

What is the preferred coordination site of CI3+? Recent computational work suggested the iodine atoms of the Lewis acid CI3+ to be more electrophilic than the classically expected carbon atom, e.g. the complex with water is of type I2C-I...OH2+ and not the classically expected I3C-OH2+. If this structure is correct, one may also anticipate reactions of CI3+ as an I+ donor. Thus, we were interested in investigating the chemistry of CI3+ in the room-temperature stable salt [CI3]+[pftb](-) ([pftb](-) = [Al(OC(CF3)3)4]-) with weak nucleophiles that i) mimic water (OEt2) or ii) are electronically deactivated weak nucleophiles (PX3, X = Cl-I; AsI3). One question was: is it possible to obtain iodine-coordinated Lewis acid-base adducts of the CI3+ cation? With Et2O as a base, the cation behaves as a strong Lewis acid and cleaves the ether to give I3C-OEt, C2H4 and [H(Et2O)2]+. By contrast PX3 and AsI3 coordinate to the CI3+ cations and the adducts have classical, carbon-bound ethane-like structures, as proven by X-ray single-crystal diffraction, IR, UV-Vis and NMR spectroscopy. From variable temperature 13C NMR studies, it followed for the I3C-AsI3+ salt that the equilibrium between CI3+ and AsI3 is reversible and temperature dependent in solution. The I3C-PI3+ salt decomposes at room temperature giving PI4+ and C2I4, likely through an iodine coordinated I2C-I[dot dot dot]PI3+ intermediate. Thus CI3+ may also act as an I+ donor. All reactions are in agreement with ab initio quantum chemical calculations at the MP2/TZVPP level and assignments of experimental spectra were aided by quantum chemistry.     

Combined experimental/theoretical investigation of the He+ICl interactions. I. Rovibronic spectrum of He...ICl complexes in the ICl B-X, 3-0 region

Transitions of two different stereoisomers of the He...ICl(X,v" = 0) weakly bound complex, one with a T-shaped orientation and another that is most likely linear, have been observed in laser-induced fluorescence experiments performed in the ICl B-X region. Here we present experimental and theoretical results aimed at confirming the previous assignments and at gaining additional insights into the He+ICl interactions. High resolution action spectra were recorded in the same region to identify those features that could be attributed to transitions of the He...I35Cl(X,v" = 0) isomers and not to higher-order complexes, Hen...I35Cl, where n > or = 2, or I37Cl containing species. Calculations of the rovibronic spectra of the He...I35Cl complexes in the ICl B-X, 2-0 and 3-0 regions were performed using an ab initio potential energy surface for the He+ICl(X,v" = 0) ground state and two different pairwise additive potentials for the He+ICl(B,v' = 2,3) excited states. The rotation-vibration energies and wave functions for the He cdots, three dots, centered I35Cl complexes were obtained for all bound states with total angular momentum J < 10 using both of these potentials. Electronic spectra were generated using these results, assuming that the transition moment lies along the ICl bond and is not perturbed by the presence of the helium atom. The calculations qualitatively reproduce the He cdots, three dots, centered I35Cl action spectrum and strongly support the previous assignments. The calculations also indicate that some of the spectral congestion observed near the linear band may be attributed to transitions of the linear isomer to multiple intermolecular levels in the excited state. Coriolis coupling strongly mixes He cdots, three dots, centered ICl(B,v') states with rotational excitation, making simulations and assignments of the linear band observed in the experimental spectrum difficult.     

A 193 nm laser photofragmentation time-of-flight mass spectrometric study of chloroiodomethane

The photodissociation dynamics of chloroiodomethane (CH2ICl) at 193 nm has been investigated by employing the photofragment time-of-flight (TOF) mass spectrometric method. Using tunable vacuum ultraviolet undulator synchrotron radiation for photoionization sampling of nascent photofragments, we have identified four primary dissociation product channels: CH2Cl + I(2P(1/2))/I(2P(3/2)), CH2I + Cl(2P(1/2))/Cl(2P(3/2)), CHI + HCl, and CH2 + ICl. The state-selective detection of I(2P(3/2)) and I(2P(1/2)) has allowed the estimation of the branching ratio for I(2P(1/2)):I(2P(3/2)) to be 0.73:0.27. Theoretical calculations based on the time-dependent density-functional theory have been also made to investigate excited electronic potential-energy surfaces, plausible intermediates, and transition structures involved in these photodissociation reactions. The translation energy distributions derived from the TOF measurements suggest that at least two dissociation mechanisms are operative for these photodissociation processes. One involves the direct dissociation from the 2 1A' state initially formed by 193 nm excitation, leading to significant kinetic-energy releases. For the I-atom and Cl-atom elimination channels, the fragment kinetic-energy releases observed via this direct dissociation mechanism are consistent with those predicted by the impulsive dissociation models. Other mechanisms are likely predissociative or statistical in nature from the lower 1 1A' and 1 1A' states and/or the ground X 1A' state populated by internal conversion from the 2 1A' state. On the basis of the maximum kinetic-energy release for the formation of CH2Cl + I(2P(1/2)), we have obtained a value of 53+/-2 kcal/mol for the 0 K bond dissociation energy of I-CH2Cl. The intermediates and transition structures for the CHI + HCl and CH2 + ICl product channels have been also investigated by ab initio quantum calculations at the MP2(full)/6-311G(d) and B3LYP(full)/6-11G(d) levels of theory. The maximum kinetic-energy releases observed for the CHI + HCl and CH2 + ICl channels are consistent with the interpretation that the formation of CHI and CH2 in their ground triplet states is not favored.     

Chemical selectivity in the remote abstractive chemisorption of ICl on Al(111)

The interaction of ICl and Al(111) involves remote dissociation in its chemisorption process. In remote dissociation, an electron harpoons from an Al(111) surface to an ICl gas molecule to initiate the chemisorption process. We have determined that ICl can chemisorb onto Al(111) by non-activated direct chemisorption, and the sticking probability of this direct channel is 0.65 +/- 0.03. Furthermore, low energy ICl molecules that do not undergo remote dissociation can chemisorb onto Al(111) by precursor-mediated chemisorption. Not only is the interaction of ICl and Al(111) reactive, it is chemically selective. Studies with Auger spectroscopy reveal that the ratio of chlorine atoms to iodine atoms on the Al(111) is 0.32 +/- 0.10 at low (0.042 +/- 0.002) surface coverage. Time-of-flight mass spectrometry studies also show that chlorine atoms are the only species scattered from the surface after ICl interacts with Al(111). These results indicate that iodine-selective abstraction, in which the iodine atom of ICl chemisorbs to the aluminium surface while the chlorine atom is ejected into the gas phase, is the dominant mechanism in this reaction. Iodine-end first collisions are more reactive than chlorine-end first collisions because the lowest unoccupied molecular orbital (LUMO) of ICl is primarily composed of iodine atomic orbitals, and it is the LUMO that interacts with the harpooning electron from the aluminium.     

New members of an old family: isolation of IC(O)Cl and IC(O)Br and evidence for the formation of weakly bound Br*...CO

The photochemically induced reactions of a dihalogen, XY, with CO isolated together in an Ar matrix at about 15 K lead to the formation of carbonyl dihalide molecules XC(O)Y, where X and Y may be the same or different halogen atoms, Cl, Br, or I. In addition to the known compounds OCCl2, OCBr2, and BrC(O)Cl, the carbonyl iodide chloride, IC(O)Cl, and carbonyl iodide bromide, IC(O)Br, compounds have thus been identified for the first time as products of the reactions involving ICl and IBr, respectively. The first product to be formed in reactions with Cl2, BrCl, or ICl is the ClCO* radical, which reacts subsequently with a second halogen atom to give the corresponding carbonyl dihalide [OCCl2, BrC(O)Cl, or IC(O)Cl]. The analogous reaction with Br2 affords, in low yield, the unusually weakly bound BrCO* radical, better described as a van der Waals complex, Br*...CO. The changes have been followed and the products characterized experimentally by their infrared spectra, and the spectra have been analyzed in light of the results afforded by ab initio (Hartree-Fock and Moeller-Plesset second-order) and density functional theory calculations.     

Reaktionen silylierter Phosphanimine mit Iodmonochlorid und Iodtrichlorid. Die Kristallstrukturen von [Me3SiNPMe3 · ICl], [Ph3PNCl · ICl] und [Me3PN(H)PMe3] [ICl2]2

Reactions of Silylated Phosphorane Imines with Iodine Monochloride and Iodine Trichloride. The Crystal Structures of [Me₃SiNPMe₃ · ICl], [Ph₃PNCl · ICl], and [Me₃PN(H)PMe₃][ICl₂]₂ The donor-acceptor complex [Me₃SiNPMe₃ · ICl] has been prepared from Me₃SiNPMe₃ and ICl in acetonitrile solution forming yellow-orange crystals. [Ph₃PNCl · ICl] can be prepared by the reaction of Me₃SiNPPh₃ with ICl₃ in dichloromethane solution forming pale yellow crystals. [Me₃PN(H)PMe₃][ICl₂]₂ is formed in a small amount by a slow reaction of Me₃SiNPMe₃ with ICl₃ in CCl₄ suspension in the presence of traces of moisture. All samples are characterized by IR spectroscopy and by X-ray structure analyses. [Me₃SiNPMe₃ · ICl] (1) : Space group Iba2, Z = 8, structure solution with 1 727 observed unique reflections, R = 0.051. Lattice dimensions at ?60°C: a = 1 510.7, b = 1 862.8, c = 988.9 pm. 1 has a molecular structure in which the N atom of the phosphorane imine is connected with the iodine atom of the ICl molecule in a linear arrangement N? I? Cl. Bond lengths N? I = 222.7 pm, I? Cl = 265.1 pm. [Ph₃PNCl · ICl] (2) : Space group Pna2₁, Z = 4, structure solution with 1 530 observed unique reflections, R = 0.030. Lattice dimensions at 20°C: a = 1 522.8, b = 1 408.3, c = 865.8 pm. 2 has a molecular structure in which the N atom of the N chlorophosphorane imine is connected with the iodine atom of the ICl molecule in a linear arrangement. Bond lengths N? Cl = 174.4 pm, N? I = 229.5 pm, I? Cl = 251.2 pm. [Me₃PN(H)PMe₃][ICl₂]₂ (3) : Space group P2₁/c, Z = 4, structure solution with 1 989 observed unique reflections, R = 0.029. Lattice dimensions at ?50°C: a = 1 223.1, b = 1 090.2, c = 1 482.8 pm, β = 112.21°. 3 consists of [Me₃PN(H)PMe₃]²⁺ ions and ICl₂^? anions. The PNP bond angle of the dication amounts to 134.4° with PN distances of 165.6 and 166.1 pm, approximately according to double bonds.     

A study of the atmospherically important reactions between dimethyl selenide (DMSe) and molecular halogens (X2 = Cl2, Br2, and I2) with ab initio calculations

The atmospherically relevant reactions between dimethyl selenide (DMSe) and the molecular halogens (X(2) = Cl(2), Br(2), and I(2)) have been studied with ab initio calculations at the MP2/aug-cc-pVDZ level of theory. Geometry optimization calculations showed that the reactions proceed from the reagents to the products (CH(3)SeCH(2)X + HX) via three minima, a van der Waals adduct (DMSe:X(2)), a covalently bound intermediate (DMSeX(2)), and a product-like complex (CH(3)SeCH(2)X:HX). The computed potential energy surfaces are used to predict what molecular species are likely to be observed in spectroscopic experiments such as gas-phase photoelectron spectroscopy and infrared matrix isolation spectroscopy. It is concluded that, for the reactions of DMSe with Cl(2) and Br(2), the covalent intermediate should be seen in spectroscopic experiments, whereas, in the DMSe + I(2) reaction, the van der Waals adduct DMSe:I(2) should be observed. Comparison is made with previous related calculations and experiments on dimethyl sulfide (DMS) with molecular halogens. The relevance of the results to atmospheric chemistry is discussed. The DMSeX(2) and DMSe:X(2) intermediates are likely to be reservoirs of molecular halogens in the atmosphere which will lead on photolysis to ozone depletion.     

Photofragment translational spectroscopy of ICl near 304 and 280 nm: Observation of an intense hot band effect

The photodissociation dynamics of ICl has been studied near 304 and 280 nm on a simple miniature time of flight (mini-TOF) photofragment translational spectrometer with a short pulse of a weak acceleration field. An intense hot band effect was observed. Many small peaks were resolved in each photofragment translational spectrum (PTS). Based on simulations, the principal peaks were assigned not only to the different photodissociation channels (1) I + Cl, (2) I + Cl*, (3) I* + Cl, or (4) I* + Cl*, but also to the different chlorine isotopes (35Cl and Cl). Moreover, some extra peaks showed the existence of an intense hot 37 band effect from vibrationally excited ICl molecules, though only a few percent of ICl molecules remained in the vibrationally excited states in our supersonic molecular beam. Based on the spectra near 304 nm, the quantum yield Ф of each channel, the curve crossing, and the branching fraction σ from each transition state were determined.     

31P CP-MAS NMR,Vibrational, and X-Ray Characterization of the Adducts of Triphenylphosphine Sulfide with ICl and IBr

The reactions between triphenylphosphine sulfide (Ph₃PS) and ICl in CCl₄ and IBr in CH₂Cl₂ in 1 : 1 molar ratio give the solid adducts Ph₃PS · ICl ( I ) and Ph₃PS · IBr ( II ) whose structures have been solved by X-ray diffraction. Compounds I and II consist of discrete molecule units and feature the S–I–Cl or S–I–Br linear group. The S–I bond distances in I , II (2.641(1), 2.665(1) Å respectively) and in compound 2 Ph₃PS · 3 I₂ ( III ) (2.729(2) Å) are correlable to the net increase in the I–X (X = Cl, Br, I) bond distance. The structural features of I , II and III are in accordance with ³¹P CP–MAS NMR, FT-Raman and FT-IR spectral data, and elucidate the nature of the donor (Ph₃PS)-acceptor (ICl, IBr, I₂) interaction.     

Heterogeneous reactions of HOI, ICl and IBr on sea salt and sea salt proxies

The heterogeneous chemistry of HOI, ICl and IBr on sea salt and sea salt proxies has been studied at 274 K using two experimental approaches: a wetted wall flow tube coupled to an electron impact mass spectrometer (WWFT-MS) and an aerosol flow tube (AFT) coupled to a differential mobility analyser (DMA) and a chemical ionisation mass spectrometer (CIMS). Uptake of all three title molecules into bulk aqueous halide salt films was rapid and controlled by gas phase diffusion. Uptake of HOI gave rise to gas-phase ICl and IBr, with the latter being the predominant product whenever Br(-) was present. Only partial release of IBr was observed due to high solubility of dihalogens in the film. ICl uptake gave the same yield of IBr as HOI uptake. Uptake of ICl on NaBr aerosol was accommodation limited with alpha = 0.018 +/- 0.004 and gas phase IBr product has a yield of 0.6 +/- 0.3. The results show that HOI can act as a catalyst for activation of bromine from sea-salt aerosols in the marine boundary layer, via the reactions: HOI(aq) + Cl + H--> ICl(aq) + H(2)O(l) and ICl(aq) + Br--> IBr(aq) + Cl.     

Dependence of the electronic absorption spectra of aqueous solutions of iodine monochloride on the conditions of dilution and storage time

The electronic absorption spectra of aqueous solutions of iodine monochloride ICl are studied. The spectra of as-prepared solutions display the absorption band associated with hydrated ICl molecules. An additional band indicating that molecular iodine was formed in the solution emerges in the spectrum as dissolution takes place. Only the band belonging to iodine monochloride remains in the absorption spectra, and no additional bands appear after chloride anions Cl^? are added to the solution. The absorption spectrum becomes more complex when ICl is dissolved in an alkaline medium. The band belonging to molecular iodine emerges in the spectra at low alkali concentrations, while being transformed to other shorter-wavelength bands at high alkali concentrations (рН ≥ 12).     

Cl_2 2HI=2HCl I_2反应机理的理论研究

分别在MP2/3-21G!!、CCSD(T)/3-21G!!//MP2/3-21G!!和B3LYP/3-21G!!3种水平上,计算研究了气相反应Cl2 2HI=2HCl I2的机理,求得一系列四中心和三中心的过渡态.通过比较六种反应通道的活化能大小,得到了相同的结论:双分子基元反应Cl2 HI"HCl ICl和ICl HI"I2 HCl的最小活化能小于Cl2、HI和ICl的解离能,从理论上证明了反应Cl2 2HI=2HCl I2将优先以分子与分子作用形式分两步完成.用内禀反应坐标(IRC)验证了MP2/3-21G!!方法计算得到的过渡态.     

Mixed quantum-classical molecular dynamics analysis of the molecular-level mechanisms of vibrational frequency shifts

A detailed analysis of the origins of vibrational frequency shifts of diatomic molecules (I2 and ICl) in a rare gas (Xe) liquid is presented. Specifically, vibrationally adiabatic mixed quantum-classical molecular dynamics simulations are used to obtain the instantaneous frequency shifts and correlate the shifts to solvent configurations. With this approach, important mechanistic questions are addressed, including the following: How many solvent atoms determine the frequency shift? What solvent atom configurations lead to blue shifts, and which lead to red shifts? What is the effect of solute asymmetry? The mechanistic analysis can be generally applied and should be useful in understanding what information is provided by infrared and Raman spectra about the environment of the probed vibrational mode.     

Cl2+2HI=2HCl+I2反应机理的理论研究

分别在MP2/3-21G**、CCSD(T)/3-21G**//MP2/3-21G**和B3LYP/3-21G**3种水平上, 计算研究了气相反应Cl₂+2HI=2HCl+I₂的机理, 求得一系列四中心和三中心的过渡态. 通过比较六种反应通道的活化能大小, 得到了相同的结论：双分子基元反应Cl₂+HIHCl+ICl和ICl+HII₂+HCl的最小活化能小于Cl₂、HI和ICl的解离能, 从理论上证明了反应Cl₂+2HI=2HCl+I₂将优先以分子与分子作用形式分两步完成. 用内禀反应坐标(IRC)验证了MP2/3-21G**方法计算得到的过渡态.     

Probing the dependence of long-range, four-atom interactions on intermolecular orientation: 2. Molecular deuterium and iodine monochloride

Laser-induced fluorescence and action spectroscopy experiments have identified multiple conformers of the D2...ICl van der Waals complex for both ortho-D2 (o-D2) and para-D2 (p-D2). As with the analogous H2...ICl van der Waals complexes [Darr, J. P.; Crowther, A. C.; Loomis, R. A.; Ray, S. E.; McCoy, A. B. J. Phys. Chem. A 2007, 111, 13387], the C2v conformer with the deuterium molecule localized at the iodine atom end of the dihalogen is significantly more stable than the asymmetric conformer that has the deuterium positioned orthogonally to the ICl bond axis, D0' = 223.9(2.4) versus 97.3(8)-103.9(3) cm(-1) for p-D2...I(35)Cl(X, v'=0). For both conformers, complexes containing p-D2 are found to be more strongly bound than those with o-D2. The electronically excited D2...ICl(A, v') and D2...ICl(B, v') complexes are found to have equilibrium geometries that are nearly the same as those of the ground-state asymmetric structures. Calculated D2...ICl(B, v'=3) energies and probability amplitudes obtained using a simple scaled He + ICl(B, v'=3) potential provide clues to the nature of the different excited-state levels accessed.     

In Process Citation

Nitron dichloroiodide-Nt(ICl(2))-has been prepared and studied, and a gravimetric determination of iodine as Nt(ICl)(2) has been based on the result. For 4-40 mg of iodine the error is less than that of the determination as AgI. Bromate and chlorate do not interfere.