Why Do Relative Intensities of Charge Transfer and Intra-4f Transitions of Eu3+ Ion Invert in Yttrium Germanate Hosts? Unravelling the Underlying Intricacies from Experimental and Theoretical Investigations.

The dominant intensity of parity-forbidden intra-4f transitions of europium(III) over O → Eu charge-transfer band (CTB) intensity is against common perceptions, yet this trend is observed in many germanate hosts and has not been rationalized so far. In search of a plausible explanation for this unusual trend, present work reports an experimental and theoretical investigations in conjunction on two sibling germanate host, namely, Y2GeO5 and Y2Ge2O7 having dopant Eu3+ in their respective YO7 polyhedra. Whereas for Y2GeO5:Eu3+, the CTB is more intense than the intra-4f transitions in the excitation spectrum, in the case of Y2Ge2O7:Eu3+, the relative intensities of CTB and intra-4f transitions are reversed. Comparative structural analysis reveals that Eu3+ present in YO7 of Y2GeO5 has a greater number of tetra-coordinated oxygen (Otetra) and yttrium atom as first and second neighbors, respectively (Eu3+-Otetra-Y3+ linkages). Conversely, in Y2Ge2O7 host, the Eu3+ ion mostly has tricoordinated oxygen (Otri) as its nearest neighbor and germanium ions next to Otri (Eu3+-Otri-Ge4+ linkage). Theoretical calculations reveal that while Y2GeO5:Eu has Otetra(4Y) dominating at the Fermi level and the 4f state of Eu3+ remains inert toward mixing, in Y2Ge2O7:Eu, the Fermi level has major contribution from Otri(2Y + 1Ge) with significant mixing with 4f states of Eu. The dominant control of Eu3+-Otri-Ge4+ linkages in geometrical and electronic structure of Y2Ge2O7:Eu owing to the GeO4 surrounding has been attributed to relative poor intensity of O → Eu CTB. Siege of Eu3+ by GeO4 and subsequent occurrence of Eu3+-Otri-Ge4+ linkages play a dual role: First, it induces electronic rigidity to hinder excitation of electron at bridging (Otri) oxygen by highly charged small Ge4+ cation; second, the covalent character in Eu-O bond is achieved by intermixing of Eu's 4f and Otri 2p orbital which facilitates relaxing of the parity-selection rule thus enhancing the probability of intra-4f transitions. The inferences drawn remain valid when extrapolated to other inorganic oxides having EuOx polyhedra surrounded by covalent units like PO4, SiO4, etc. and have a prevailing number of low-coordinated oxygen atoms and highly charged small cation in the first and second coordination shells, respectively. The optical basicity concept is also found to endorse our explanation. These remarkable generic inferences will pave the rational way for designing efficient phosphors for solid-state lighting.

Disappearance and recovery of luminescence in Bi3+, Eu3+ codoped YPO4 nanoparticles due to the presence of water molecules up to 800 °C.

YPO(4) nanoparticles codoped with Eu(3+) (5 at. %) and Bi(3+) (2-10 at. %) have been synthesized by a simple coprecipitation method using a polyethylene glycol-glycerol mixture, which acts as capping agent. It has been found that the incorporation of Bi(3+) ions into the YPO(4):Eu(3+) lattice induces a phase transformation from tetragonal to hexagonal, and also a significant decrease in Eu(3+) luminescence intensity was observed. This is related to the association of the water molecules in the hexagonal phase of YPO(4) in which the nonradiative process from the surrounding water molecules around Eu(3+) is dominating over the radiative process. On annealing above 800 °C, luminescence intensity recovers due to significant removal of water. 900 °C annealed Bi(3+) codoped YPO(4):Eu(3+) shows enhanced luminescence (2-3 times) as compared to that of YPO(4):Eu(3+). When sample was prepared in D(2)O (instead of H(2)O), 4-fold enhancement in luminescence was observed, suggesting the extent of reduction of multiphonon relaxation in D(2)O. This study illustrates the stability of water molecules even at a very high temperature up to 800 °C in Eu(3+) and Bi(3+) codoped YPO(4) nanoparticles.

Multiphoton ionization and Coulomb explosion of C2H5Br clusters: a mass spectrometric and charge density study.

Using time-of-flight mass spectrometry (TOFMS), laser-induced photochemistry of ethyl bromide clusters has been investigated at three different wavelengths (viz. 266, 355 and 532 nm) utilizing nanosecond laser pulses of ~5 × 10(9) W/cm(2). An interesting finding of the present work is the observation of multiply charged atomic ions of carbon and bromine at 355 and 532 nm, arising from the Coulomb explosion of (C(2)H(5)Br)(n) clusters. At 266 nm, however, the (C(2)H(5)Br)(n) clusters were found to exhibit the usual multiphoton dissociation/ionization behaviour. The TOFMS studies are complemented by measuring the total charge density of the ionized volume at 266, 355 and 532 nm, using the parallel plate method, and the charge densities were found to be ~2 × 10(9), 6 × 10(9) and 2 × 10(11) charges/cm(3), respectively. The significantly higher charge density and the presence of energetic, multiply charged atomic ions at 532 nm are explained by the higher ponderomotive energy of the 532 nm photon, coupled with the Coulomb stability of the residual multiply charged ethyl bromide clusters generated upon laser irradiation, due to their larger effective cluster size at 532 nm than at 355 and 266 nm.

Effects of Ce3+ codoping and annealing on phase transformation and luminescence of Eu3+-doped YPO4 nanorods: D2O solvent effect.

Ce(3+)- and Eu(3+)-doped YPO(4) nanorods have been prepared at relatively low temperature (120 degrees C). A detailed investigation of the role of Ce(3+) concentration up to 10 atom % on the luminescence intensity of Eu(3+) in Ce(3+)- and Eu(3+)-doped YPO(4) has been carried out. Phase transformation from a tetragonal to a hexagonal structure occurs with increasing Ce(3+) concentrations, and water molecules are also associated during phase transformation. Thermal study shows that water can be retained up to 800 degrees C in the hexagonal structure. Interestingly, the hexagonal structure returns to the tetragonal structure on annealing above 900 degrees C. As-prepared and 500 degrees C heated samples show uniform sized nanorods, whereas a 900 degrees C heated sample shows distorted nanorods in which pores are present. Initially, the luminescence intensity decreases sharply with increasing Ce(3+) concentrations, even for 2 atom %. This is related to the enhanced nonradiative rate as compared to the radiative rate, since multiphonon relaxation to surrounding water molecules increases. This is not due to the possible oxidation-reduction process between Eu(3+) and Ce(3+) to give Eu(2+) and Ce(4+), as confirmed by X-ray photoelectron spectroscopy and luminescence studies. Then, a significant enhancement of luminescence intensity occurs on annealing above 900 degrees C. This can be ascribed to the loss of water molecules during a phase transformation from the hydrated hexagonal to the dehydrated tetragonal phase. To the authors' knowledge, we for the first time performed a luminescent study with a change of solvent from H(2)O to D(2)O, and significant enhancement in luminescence is found.

Ultraviolet photochemistry of buta-1,3- and buta-1,2-dienes: laser spectroscopic absolute hydrogen atom quantum yield and translational energy distribution measurements.

Using pulsed H-atom Lyman-alpha laser-induced fluorescence spectroscopy along with a photolytic calibration approach, absolute H-atom product quantum yields of phi(H-b13d) = (0.32+/-0.04) and phi(H-b12d) = (0.36+/-0.04) were measured under collision-free conditions for the 193 nm gas-phase laser flash photolysis of buta-1,3- and buta-1,2-diene at room temperature, which demonstrate that nascent H-atom formation is of comparable importance for both parent molecules. Comparison of the available energy fraction, f(T-b13d) = (0.22+/-0.03) and f(T-b12d) = (0.13+/-0.01), released as H+C(4)H(5) product translational energy with results of impulsive and statistical energy partitioning modeling calculations indicates that for both, buta-1,3- and buta-1,2-diene, H-atom formation is preceded by internal conversion to the respective electronic ground state (S(0)) potential energy surfaces. In addition, values of sigma(b-1,3-d-L alpha) = (3.5+/-0.2)x10(-17) cm(2) and sigma(b-1,2-d-L alpha) = (4.4+/-0.2)x10(-17) cm(2) for the previously unknown Lyman-alpha (121.6 nm) radiation photoabsorption cross sections of buta-1,3- and buta-1,2-diene in the gas-phase were determined.

Luminescence studies on low temperature synthesized ZnGa2O4:Ln3+ (Ln = Tb and Eu) nanoparticles.

ZnGa2O4 nanoparticles doped with lanthanide ions (Tb3+ and Eu3+) were prepared at a low temperature of 120 degrees C based on urea hydrolysis in ethylene glycol medium. X-ray diffraction studies have confirmed that strain associated with nanoparticles changes as Tb3+ gets incorporated in the ZnGa2O4 lattice. Based on steady state emission and excitation studies of ZnGa2O4:Tb nanoparticles, it has been inferred that ZnGa2O4 host is characterized by a broad emission around 427 nm and there exists energy transfer between the host and Tb3+ ions. Unlike this, for ZnGa2O4:Eu nanoparticles, very poor energy transfer between the host and Eu3+ ions is observed. These nanoparticles when coated with ligands like oleic acid results in their improved dispersion in organic solvents like chloroform and dichloromethane.

Synthesis and characterization of monodispersed water dispersible Fe3O4 nanoparticles and in vitro studies on human breast carcinoma cell line under hyperthermia condition.

Monodispersed Fe3O4 magnetic nanoparticles (MNPs) having size of 7 nm have been prepared from iron oleate and made water dispersible by functionalization for biomedical applications. Three different reactions employing thioglycolic acid, aspartic acid and aminophosphonate were performed on oleic acid coated Fe3O4. In order to achieve a control on particle size, the pristine nanoparticles were heated in presence of ferric oleate which led to increase in size from 7 to 11 nm. Reaction parameters such as rate of heating, reaction temperature and duration of heating have been studied. Shape of particles was found to change from spherical to cuboid. The cuboid shape in turn enhances magneto-crystalline anisotropy (Ku). Heating efficacy of these nanoparticles for hyperthermia was also evaluated for different shapes and sizes. We demonstrate heat generation from these MNPs for hyperthermia application under alternating current (AC) magnetic field and optimized heating efficiency by controlling morphology of particles. We have also studied intra-cellular uptake and localization of nanoparticles and cytotoxicity under AC magnetic field in human breast carcinoma cell line.

Bimetallic Wiregauze Supported Pt-Ru Nanocatalysts for Hydrogen Mitigation.

Passive autocatalytic recombiner (PAR) is one of the most suitable devices for mitigation of hydrogen, generated in nuclear power plant under accidental conditions. For this purpose we report development of stainless steel wire gauze supported Pt-Ru nanoparticles as catalysts. Simultaneous electroless deposition has been employed for the synthesis of the catalysts. Pt-Ru based bimetallic catalysts were characterized for their rate of coating kinetics, noble metal loading, phase purity by XRD and surface morphology by SEM, TEM and elemental analysis by SIMS. Developed catalysts were found to be active for efficient recombination of hydrogen and oxygen in air as well as in presence of various prospective poisons like CO2, CH4, CO and relative humidity. Pt-Ru based bimetallic catalyst with 0.9% loading was found to be active for CO poisoning up to 400 ppm of CO.

Covalent bridging of surface functionalized Fe3O4 and YPO4:Eu nanostructures for simultaneous imaging and therapy.

Magnetic luminescent hybrid nanostructures (MLHN) have received a great deal of attention due to their potential biomedical applications such as thermal therapy, magnetic resonance imaging, drug delivery and intracellular imaging. We report the development of bifunctional Fe3O4 decorated YPO4:Eu hybrid nanostructures by covalent bridging of carboxyl PEGylated Fe3O4 and amine functionalized YPO4:Eu particles. The surface functionalization of individual nanoparticulates as well as their successful conjugation was evident from Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), zeta-potential and transmission electron microscopy (TEM) studies. X-ray diffraction (XRD) analysis reveals the formation of highly crystalline hybrid nanostructures. TEM micrographs clearly show the binding/anchoring of 10 nm Fe3O4 nanoparticles onto the surface of 100-150 nm rice grain shaped YPO4:Eu nanostructures. These MLHN show good colloidal stability, magnetic field responsivity and self-heating capacity under an external AC magnetic field. The induction heating studies confirmed localized heating of MLHN under an AC magnetic field with a high specific absorption rate. Photoluminescence spectroscopy and fluorescence microscopy results show optical imaging capability of MLHN. Furthermore, successful internalization of these MLHN in the cells and their cellular imaging ability are confirmed from confocal microscopy imaging. Specifically, the hybrid nanostructure provides an excellent platform to integrate luminescent and magnetic materials into one single entity that can be used as a potential tool for hyperthermia treatment of cancer and cellular imaging.

Bi-functional properties of Fe3O4@YPO4:Eu hybrid nanoparticles: hyperthermia application.

Magnetic nanoparticles based hyperthermia therapy is a possible low cost and effective technique for killing cancer tissues in the human body. Fe3O4 and Fe3O4@YPO4:5Eu hybrid magnetic nanoparticles are prepared by co-precipitation method and their average particle sizes are found to be ∼10 and 25 nm, respectively. The particles are spherical, non-agglomerated and highly dispersible in water. The crystallinity of as-prepared YPO4:5Eu sample is more than Fe3O4@YPO4:5Eu hybrid magnetic nanoparticles. The chemical bonds interaction between Fe3O4 and YPO4:5Eu is confirmed through FeO-P. The magnetization of hybrid nanocomposite shows magnetization Ms = 11.1 emu g(-1) with zero coercivity (measured at 2 × 10(-4) Oe) at room temperature indicating superparamagnetic behaviour. They attain hyperthermia temperature (~42 °C) under AC magnetic field showing characteristic induction heating of the prepared nanohybrid and they will be potential material for biological application. Samples produce the red emission peaks at 618 nm and 695 nm, which are in range of biological window. The quantum yield of YPO4:5Eu sample is found to be 12%. Eu(3+) present on surface and core could be distinguished from luminescence decay study. Very high specific absorption rate up to 100 W g(-1) could be achieved. The intracellular uptake of nanocomposites is found in mouse fibrosarcoma (Wehi 164) tumor cells by Prussian blue staining.

Synthesis of oleic acid functionalized Fe3O4 magnetic nanoparticles and studying their interaction with tumor cells for potential hyperthermia applications.

In the present study, oleic acid (OA) functionalized Fe3O4 magnetic nanoparticles (MN) were synthesized following modified wet method of MN synthesis. The optimum amount of OA required for capping of MN and the amount of bound and unbound/free OA was determined by thermogravimetric analysis (TGA). Further, we have studied the effect of water molecules, associated with MN, on the variation in their induction heating ability under alternating current (AC) magnetic field conditions. We have employed a new approach to achieve dispersion of OA functionalized MN (MN-OA) in aqueous medium using sodium carbonate, which improves their biological applicability. Interactions amongst MN, OA and sodium carbonate were studied by Fourier transform infrared spectroscopy (FT-IR). Intracellular localization of MN-OA was studied in mouse fibrosarcoma cells (WEHI-164) by prussian blue staining and confocal laser scanning microscopy (CLSM) using nile blue A as a fluorescent probe. Results showed MN-OA to be interacting mainly with the cell membrane. Their hyperthermic killing ability was evaluated in WEHI-164 cells by trypan blue method. Cells treated with MN-OA in combination with induction heating showed decreased viability as compared to respective induction heating controls. These results were supported by altered cellular morphology after treatment of MN-OA in combination with induction heating. Further, the magnitude of apoptosis was found to be ~5 folds higher in cells treated with MN-OA in combination with induction heating as compared to untreated control. These results suggest the efficacy of MN-OA in killing of tumor cells by cellular hyperthermia.

Multicolored and white-light phosphors based on doped GdF3 nanoparticles and their potential bio-applications.

Rare-earth-doped gadolinium fluoride nanocrystals were synthesized by a single step synthesis employing ethylene glycol as solvent. Based on X-ray diffraction studies, stabilization of hexagonal modification of GdF(3) has been inferred. The microscopic studies show formation of uniformly distributed nanocrystals (~15 nm). The nanoparticles are readily dispersible in water and show bright luminescence in colloidal solution. The luminescence properties have been investigated as a function of activator concentrations, and enhanced optical properties have been attributed to efficient energy transfer from the Gd(3+) to the activator RE(3+) ions, which has further been confirmed by steady-state and time-resolved optical studies. It has been demonstrated that on doping appropriate amount of activators in host GdF(3), a novel white-light-emitting phosphor is obtained with CIE co-ordinates and correlated color temperature (CCT) very close to broad daylight. This can have promising applications as phosphor for white-light ultraviolet-light-emitting diodes (UV-LEDs). Our experiments showed efficient labeling of human breast carcinoma cells (MCF-7) by Tb(3+)-doped GdF(3) nanoparticles. The fluorescence intensity was found to be dependent on the surface modifying/coating agent, and the results were validated using confocal microscopy in terms of localization of these functionalized nanoparticles.

Re-dispersion and film formation of GdVO4 : Ln3+ (Ln3+ = Dy3+, Eu3+, Sm3+, Tm3+) nanoparticles: particle size and luminescence studies.

GdVO(4) : Ln(3+) (Ln(3+) = Dy(3+), Eu(3+), Sm(3+), Tm(3+)) nanoparticles are prepared by a simple chemical route at 140 °C. The crystallite size can be tuned by varying the pH of the reaction medium. Interestingly, the crystallite size is found to increase significantly when pH increases from 6 to 12. This is related to slower nucleation of the GdVO(4) formation with increase of VO(4)(3-) present in solution. The luminescence study shows an efficient energy transfer from vanadate absorption of GdVO(4) to Ln(3+) and thereby enhanced emissions are obtained. A possible reaction mechanism at different pH values is suggested in this study. As-prepared samples are well dispersed in ethanol, methanol and water, and can be incorporated into polymer films. Luminescence and its decay lifetime studies confirm the decrease in non-radiative transition probability with the increase of heat treatment temperature. Re-dispersed particles will be useful in potential applications of life science and the film will be useful in display devices.

Structural, luminescence and EPR studies on SrSnO3 nanorods doped with europium ions.

The present study describes the structural and luminescent properties of SrSnO(3) nanorods containing Eu(3+) ions. Based on Rietveld refinement of XRD patterns corresponding to both undoped and europium doped SrSnO(3) nanorods, it is inferred that the average bond lengths of Sr-O1 linkages, which have a square planar geometry around Sr(2+) in the SrO(12) polyhedra present in SrSnO(3), remained unaffected with Eu(3+) incorporation into the lattice. However, the average bond lengths of shorter Sr-O2 linkages increase and longer Sr-O2 linkages decrease with Eu(3+) doping into the SrSnO(3) lattice. A lack of variation in the lattice parameters of SrSnO(3) with doped Eu(3+) ions is explained based on mutually compensating changes in the average bond lengths of the Sr-O2 linkages in the unit cell. Luminescence studies have confirmed that Eu(3+) ions occupy the centrosymmetric Sr(2+) site only up to 2 at%, beyond which Eu(3+) ions exist in a significantly distorted environment (grain boundaries). Beyond 3%, incorporation of Eu(3+) ions into the SrSnO(3) lattice leads to the formation of a Eu(2)Sn(2)O(7) phase. From the EPR studies it is confirmed that around 5% of the incorporated Eu(3+) ions get converted to Eu(2+) ions and they occupy Sr(2+) sites in the lattice.

Luminescence switching behavior through redox reaction in Ce3+ co-doped LaPO4:Tb3+ nanorods: re-dispersible and polymer film.

Re-dispersible Tb(3+) doped LaPO(4) nanorods have been prepared using ethylene glycol (EG) as a capping agent as well as reaction medium at a relatively low temperature of 150 °C. The X-ray diffraction study reveals that all the doped samples are well crystalline with a monoclinic structure of the LaPO(4) phase. The luminescence intensity of (5)D(4)→(7)F(5) transition at 543 nm (green) is more prominent than that of (5)D(4)→(7)F(6) transition at 487 nm (blue) for all the samples. This is related to the polarizing effect from [PO(4)](3-) to the Tb(3+) site. Concentration dependent luminescence study shows that the luminescence intensity of Tb(3+) increases up to 10 at.% and decreases above this. This is due to the concentration quenching effect arising from cross relaxation among Tb(3+)-Tb(3+) ions. The results show that nanoparticles prepared in EG medium gives an enhanced luminescence compared to that prepared in water. This is attributed to the multiphonon relaxation effect from O-H groups surrounding over nanoparticles as well as the extent of increase of agglomeration among particles for samples prepared in water. Significant enhancement in the emission of Tb(3+) is also observed when Ce(3+) is used as the sensitizer in LaPO(4):Tb(3+)nanorods. The optimum concentration of Ce(3+) for maximum luminescence is found to be 7 at.% in Ce(3+) sensitized LaPO(4):Tb(3+) (5 at.%). Based on the energy transfer process from Ce(3+) to Tb(3+), the luminescence of Tb(3+) can be switched OFF and ON by performing oxidation and reduction of Ce(3+)↔Ce(4+) using KMnO(4) and ascorbic acid, respectively. The samples are re-dispersible in water, methanol and can be incorporated into polyvinyl alcohol (PVA) films. They show a dark green emission under ultraviolet radiation.

Effect of structure, particle size and relative concentration of Eu(3+) and Tb(3+) ions on the luminescence properties of Eu(3+) co-doped Y(2)O(3):Tb nanoparticles.

Eu(3+) co-doped Y(2)O(3):Tb nanoparticles were prepared by the combustion method and characterized for their structural and luminescence properties as a function of annealing temperatures and relative concentration of Eu(3+) and Tb(3+) ions. For Y(2)O(3):Eu,Tb nanoparticles annealed at 600 and 1200 °C, variation in the relative intensity of excitation transitions between the (7)F(6) ground state and low spin and high spin 4f(7)5d(1) excited states of Tb(3+) is explained due to the combined effect of distortion around Y(3+)/Tb(3+) in YO(6)/TbO(6) polyhedra and the size of the nanoparticles. Increase in relative intensity of the 285 nm peak (spin-allowed transition denoted as peak B) with respect to the 310 nm peak (spin-forbidden transition denoted as peak A) with decrease of Tb(3+) concentration in the Y(2)O(3):Eu,Tb nanoparticles heated at 1200 °C is explained based on two competing effects, namely energy transfer from Tb(3+) to Eu(3+) ions and quenching among the Tb(3+) ions. Back energy transfer from Tb(3+) to Eu(3+) in these nanoparticles is found to be very poor.

Energy pooling in multiple ionization and Coulomb explosion of clusters by nanosecond-long, megawatt laser pulses.

We report the results of experiments that establish the possibility of bringing about multiple ionization and Coulomb explosion of molecular clusters with nanosecond laser pulses at intensities as small as 10(9) W cm(-2). We demonstrate several new facets of the laser-cluster interaction in the low-intensity, long-pulse domain: (i) The choice of laser wavelength for a given cluster species is very crucial. (ii) Excited electronic states play a very important role in the ionization dynamics. (iii) When field ionization is insignificant and ponderomotive energies are very small, it is energy pooling rather than inverse bremsstrahlung that determines how clusters absorb energy from the optical field.

Photoionization of CH(3)I mediated by the C state in the visible and ultraviolet regions.

Three/two-photon resonant multiphoton ionization (MPI) of the CH3I monomer has been studied in the gas phase at 532 and 355 nm using time-of-flight mass spectrometry. Under low laser intensity (approximately 10(9) W/cm2) the mass spectra showed peaks at m/z 15, 127 and 142, corresponding to [CH3]+, [I]+ and [CH3I]+ species, at both these wavelengths. The laser power dependence for [CH3I]+, [I]+ and [CH3]+ ions showed a three-photon dependence at 532 nm. For the same three ions, photoionization studies at 355 nm gave a power dependence of 2. Both these results suggest that a vibronic energy level at approximately 7 eV, lying in the Rydberg C state, acts as a resonant intermediate level in ionization of CH3I. In the case of 355 nm, with increasing intensity additional peaks at m/z 139 and 141 were observed which could be assigned to [CI]+ and [CH2I]+ fragments. In contrast, for high intensity radiation at 532 nm ( approximately 2 x 10(10) W/cm2), only the [CI]+ fragment was observed. At these wavelengths, fragment ions observed in mass spectra mainly arise from photodissociation of the parent ion. Experiments at another wavelength in the visible region (564.2 nm) confirmed the results obtained at 532 nm. In order to assess the role of the A state in these MPI experiments, additional experiments were performed at 266 and 282.1 nm, which access the A state directly via a one-photon transition, and showed absence of a surviving precursor ion. Reaction energies for various possible dissociation channels of CH3I/[CH3I]+/[CH2I]+ were calculated theoretically at the MP2 level using the GAMESS electronic structure program.

Multiphoton dissociation/ionization of CHCl3 and CFCl3 at 355 nm: an experimental and theoretical study.

Nonresonant laser-induced multiphoton dissociation/ionization studies have been conducted for trichloromethane (CHCl3) and trichlorofluoromethane (CFCl3) at 355 nm, using time-of-flight mass spectrometry (TOFMS). The molecular ion signal was found to be missing for both these compounds, and very similar fragmentation patterns were observed. Ab initio molecular electronic structure calculations were performed to help understand the fragmentation pattern of these molecules in the laser field. The energetics of different dissociation channels in the ground states of [CHCl3]+*, [CHCl2]+, [CFCl3]+* and [CFCl2]+, as well as neutral CHCl3, CHCl2*, CFCl3 and CFCl2* systems, were calculated. On comparing theoretical results with experimentally observed ion signals and their relative abundances in TOFMS, it is inferred that these molecules undergo sequential Cl atom elimination followed by photoionization of the fragments. The absence of [CFCl]+ has been interpreted on the basis of resonant A state-mediated two-photon absorption by CFCl, and the subsequent prompt photodissociation processes occurring for this state.