Experimental determination of energy disposal in the dissociative electron recombinations of CS2(+) and HCS2(+)

Vibronic optical emissions from CS(A1pi --> X1sigma+) and CS(a3pi --> X1sigma+) transitions have been identified from dissociative recombination (DR) of CS2(+) and HCS2(+) plasmas. All of the spectra were taken in flowing afterglow plasmas using an optical monochromator in the UV-visible wavelength region of 180-800 nm. For the CS(A --> X) and CS(a --> X) emissions, the relative vibrational distributions have been calculated for v' < 5 and v' < 3 in both types of plasmas for the CS(A) and CS(a) states, respectively. Both recombining plasmas show a population inversion from the v' = 0 to v' = 1 level of the CS(A) state, similar to other observations of the CS(A) state populations, which were generated using two other energetic processes. The possibility of spectroscopic cascading is addressed, such that transitions from upper level electronic states into the CS(A) and CS(a) states would affect the relative vibrational distribution, and there is no spectroscopic evidence supporting the cascading effect. Additionally, excited-state transitions from neutral sulfur (S(5S(2)0 --> 3P(2)) and S(5S(2)0 --> 3P(1))) and the products of ion-molecule reactions (CS(B1sigma+ --> A1pi), CS(+)(B2sigma+ --> A2pi(i)), and CS2(+) (A2pi(u) --> X2pi(g))) have been observed and are discussed.     

Investigation of spatially resolved spectra of OH and N2+ in N2 and H2O mixture wire-plate positive pulsed streamer discharge

Optical emission spectroscopy has been applied to study the spatially resolved measurements of the emission intensities of OH (A(2)Sigma-->X(2)Pi, 0-0) and N(2)(+) (B(2)Sigma(u)(+)-->X(2)Sigma(g)(+), 0-0, 391.4 nm) produced by a high-voltage positive pulsed streamer discharge consisting of a gas mixture of N(2) and H(2)O in a wire-plate reactor under severe electromagnetic interference at atmospheric pressure. The effects of pulse peak voltage, pulse repetition rate, and the added O(2) flow rate on the spatial distributions of the emission intensity of OH (A(2)Sigma-->X(2)Pi, 0-0) and N(2)(+) (B(2)Sigma(u)(+)-->X(2)Sigma(g)(+), 0-0, 391.4 nm) in the lengthwise direction (direction from wire to plate) are investigated. It has been found that the emission intensities of OH (A(2)Sigma-->X(2)Pi, 0-0) and N(2)(+) (B(2)Sigma(u)(+)-->X(2)Sigma(g)(+), 0-0, 391.4 nm) rise with an increase in both pulse peak voltage and pulse repetition rate and decrease with an increase in oxygen flows added in an N(2) and H(2)O gas mixture. The emission intensity of OH (A(2)Sigma-->X(2)Pi, 0-0) decreases with increasing the distance from the wire electrode. The emission intensity of N(2)(+) (B(2)Sigma(u)(+)-->X(2)Sigma(g)(+), 0-0, 391.4 nm) is nearly constant at 0-4mm from wire electrode, and sharply increases near the ground electrode. The vibrational temperature of N(2) (C) increases with increasing O(2) flows and keeps almost constant in the lengthwise direction under the present experimental conditions. The main physicochemical processes involved are also discussed in this paper.     

Continuum and discrete pulsed cavity ring down laser absorption spectra of Br2 vapor

The absorption cross-sections at room temperature are reported for the first time, of Br2 vapor in overlapping bound-free and bound-bound transition of A(3)pi1u <-- Xsigma(g)+, X(1)pi1u <-- X(1)sigma(g)+ and B(3)pi0u <-- X(1)sigma(g)+, using cavity ring down spectroscopy (CRDS) technique. We reported here, the A(3)pi1u <-- X(1)sigma(g)+, transition is included along with the two stronger X(1)pi1u <-- X(1)sigma(g)+ and B(3)pi0u <-- X(1)sigma(g) transitions of Br2. We obtained discrete absorption cross-section in the rotational structure, the continuum absorption cross-sections, and were also able to measure the absorption cross-section in separate contribution of A(3)pi1u <-- X(1)sigma(g)+, (1)pi1u <-- X(1)sigma(g)+, and B(3)pi0u <-- X(1)sigma(g)+ transitions using CRDS method to use quantum yield of Br*((2)P(1/2)). We obtained absorption cross-section order 10(-19) cm2 and detection 10(13) molecule cm(-3) (1 mTorr) of Br2. The absorption cross-sections are increasing with increasing excitation energy in the wavelength region 510-535 nm.     

介质阻挡放电中OH自由基对甲醛脱除的影响

对管线式介质阻挡放电中的甲醛脱除进行了实验研究, 测量了介质阻挡放电产生的OH (A²Σ→X ²Π, 0-0)自由基发射光谱. 研究了在一个大气压下不同放电峰值电压、放电频率、添加氩气和氧气时甲醛脱除率与OH自由基发射光谱强度的变化关系. 实验结果表明: 在氮气含甲醛体系中, 提高放电峰值电压、放电频率和增大氩气含量时, 甲醛脱除率随OH (A²Σ→X ²Π, 0-0)自由基发射光谱强度的增强而提高; 当在氮气含甲醛体系中增大氧气含量时, 甲醛脱除率随OH (A²Σ→X ²Π, 0-0)自由基发射光谱强度的减弱而降低. 在11.5 kV放电峰值电压和9 kHz放电频率下, 氮气含甲醛体系中甲醛脱除率达93.8%.     

Transition probabilities and average cross sections for the Na2 B1pi(u) --> X1sigma(g)+ system using as excitation the 4880 A Ar+ laser line

The fluorescence spectrum of Na2 induced by the 4879.86 A line of an Argon ion laser has been analyzed with special emphasis on determination of accurate relative intensities. We have observed nineteen fluorescence series for the B1pi(u) --> X1sigma(g)+ band system. Some series are reported for the first time. The radiative transition probabilities for the observed fluorescence series were calculated using hybrid potential energy curves for the B1pi(u) and X1sigma(g)+ states constructed up to dissociation and a B-X transition dipole moment function. Radiative lifetimes for the rovibrational levels of the upper states pumped by the laser line have also been calculated. The transition probabilities and lifetimes agree with the corresponding observed measurements usually within the experimental uncertainty. From the rotational satellite structure with deltaJ' = +/- 1, +/- 2...+/- 20, for some nu'-bands of the most intense fluorescence series induced by emission from the vibrational-rotational levels: nu' = 6, J' = 43 and v' = 9, J' = 56, collision-induced transition rates and average cross sections have been obtained.     

Electronic structure, spectroscopic properties, and reactivity of molybdenum and tungsten nitrido and imido complexes with diphosphine coligands: influence of the trans ligand

A series of molybdenum and tungsten nitrido, [M(N)(X)(diphos)2], and imido complexes, [M(NH)(X)(diphos)2)]Y, (M = Mo, W) with diphosphine coligands (diphos = dppe/depe), various trans ligands (X = N3-, Cl-, NCCH3) and different counterions (Y-= Cl-, BPh4-) is investigated. These compounds are studied by infrared and Raman spectroscopies; they are also studied with isotope-substitution and optical-absorption, as well as emission, spectroscopies. In the nitrido complexes with trans-azido and -chloro coligands, the metal-N stretch is found at about 980 cm(-1); upon protonation, it is lowered to about 920 cm(-1). The 1A1 --> 1E (n --> pi) electronic transition is observed for [Mo(N)(N3)(depe)2] at 398 nm and shows a progression in the metal-N stretch of 810 cm(-1). The corresponding 3E --> 1A (pi --> n) emission band is observed at 542 nm, exhibiting a progression in the metal-N stretch of 980 cm(-1). In the imido system [Mo(NH)(N3)(depe)2]BPh4, the n --> pi transition is shifted to lower energy (518 nm) and markedly decreases in intensity. In the trans-nitrile complex [Mo(N)(NCCH3)(dppe)2]BPh4, the metal-N(nitrido) stretching frequency increases to 1016 cm(-1). The n --> pi transition now is found at 450 nm, shifting to 525 nm upon protonation. Most importantly, the reduction of this nitrido trans-nitrile complex is drastically facilitated compared to its counterparts with anionic trans-ligands (Epred = -1.5 V vs Fc+/Fc). On the other hand, the basicity of the nitrido group is decreased (pKa{[Mo(NH)(NCCH3)(dppe)2](BPh4)2} = 5). The implications of these findings with respect to the Chatt cycle are discussed.     

A laser spectroscopic study of the X2pi(g), A2pi(u), and B2sigma+ states of BS2: Renner-Teller, spin-orbit, and K-resonance effects

The lowest-lying vibronic levels of the X, A, and B states of BS2 have been investigated at high resolution using a combination of room-temperature absorption and supersonic jet data. In both cases, the BS2 radical was prepared in an electric discharge using a precursor gas mixture of BCl3,CS2, and either helium or argon. Extensive absorption spectra were obtained for the 0(0)0 and 2(1)1 bands of the A2pi(u)-X2pi(g) electronic transition in the visible. The A-X 2(1)1 and B2sigma(u)(+)-X2pi(g) 2(1) bands of jet-cooled BS2 were also studied with laser-induced fluorescence techniques. By fitting the 0(0) bands of both electronic transitions simultaneously, we were able to precisely determine the spin-orbit splittings in both the A and X states. Similarly, the 21 bands were fitted in a merged analysis in order to determine the relative separations of the vibronic components of the ground and first excited state bending levels as accurately as possible. Due to a large spin-orbit splitting and small Renner-Teller interaction, the A state bending level shows small but definite K-resonance effects, which were fitted using a full matrix for the four components of upsilon2' = 1. The resulting parameters were used along with previously published data to refine the Renner-Teller analyses in both the A2pi(u), and X2pi(g) electronic states. Where possible, the fitted constants and observed boron isotope splittings have been shown to be in accord with theoretical estimates of their sign and magnitude.     

Manifestation of stereoelectronic effects on the calculated carbon-hydrogen bond lengths and one-bond 1J(C-H) NMR coupling constants. Relative acceptor ability of the carbonyl (C=O), thiocarbonyl (C=S), and methylidene (C=CH2) groups toward C-H donor bonds

Theoretical examination [B3LYP/6-31G(d,p), PP/IGLO-III//B3LYP/6-31G(d,p), and NBO methods] of six-membered cyclohexane 1 and carbonyl-, thiocarbonyl-, or methylidene-containing derivatives 2-27 afforded precise structural (in particular, C-H bond distances) and spectroscopic (specifically, one-bond (1)J(C)(-)(H) NMR coupling constants) data that show the consequences of stereoelectronic hyperconjugative effects in these systems. Major observations include the following. (1) sigma(C)(-)(H)(ax)() -->(C)(=)(Y) and pi(C)(=)(Y) --> sigma(C)(-)(H)(ax)() (Y = O, S, or CH(2)) hyperconjugation leads to a shortening (strengthening) of the equatorial C-H bonds adjacent to the pi group. This effect is reflected in smaller (1)J(C)(-)(H)(ax)() coupling constants relative to (1)J(C)(-)(H)(eq)(). (2) Comparison of the structural and spectroscopic consequences of sigma(C)(-)(H)(ax)() --> pi(C)(=)(Y) hyperconjugation in cyclohexanone 2, thiocyclohexanone 3, and methylenecyclohexane 4 suggests a relative order of acceptor orbital ability C=S > C=O > C=CH(2), which is in line with available pK(a) data. (3) Analysis of the structural and spectroscopic data gathered for heterocyclic derivatives 5-12 reveals some additivity of sigma(C)(-)(H)(ax)() --> pi(C)(=)(Y), pi(C)(=)(Y) --> sigma(C)(-)(H)(ax)(), n(X) --> sigma(C)(-)(H)(ax)(), n(beta)(O) --> sigma(C)(-)(H)(eq)(), and sigma(S)(-)(C) --> sigma(C)(-)(H)(eq)() stereoelectronic effects that is, nevertheless, attenuated by saturation effects. (4) Modulation of the C=Y acceptor character of the exocyclic pigroup by conjugation with alpha-heteroatoms O, N, and S in lactones, lactams, and methylidenic analogues 13-24 results in decreased sigma(C)(-)(H)(ax)() --> pi(C)(=)(Y) and pi(C)(=)(Y) --> sigma(C)(-)(H)(ax)() hyperconjugation. (5) Additivity of sigma(C)(-)(H)(ax)() --> pi(C)(=)(Y) and pi(C)(=)(Y) --> sigma(C)(-)(H)(ax)() hyperconjugative effects is also apparent in 1,3-dicarbonyl derivative 25 (C=Y equal to C=O), 1,3-dithiocarbonyl derivative 26 (C=Y equal to C=S), and 1,3-dimethylidenic analogue 27 (C=Y equal to C=CH(2)).     

Ab initio investigation of the electronic structure and bonding of the HC(N2)x(+) and HC(CO)x(+) cations, x = 1, 2

Employing the coupled-cluster approach and correlation consistent basis sets of triple and quadruple cardinality, we have investigated the electronic structure and bonding of the HC(N2)x(+) and HC(CO)x(+), x = 1, 2, molecular cations. We report geometries, binding energies and potential energy profiles. The ground states of HC(N2)+, HC(CO)+ and HC(N2)2(+), HC(CO)2(+) are of 3sigma- and 1A1 symmetries, respectively. All four charged species are well bound with binding energies ranging from 81 [HC(N2)+ (X3sigma-) --> CH+(a3pi) + N2(X1sigma(g)+)] to 178 [HC(CO)2(+)(X1A1) --> CH+(X1sigma+) + 2CO(X1sigma+)] kcal/mol. It is our belief that the X1A1 states of HC(N2)2(+) and HC(CO)2(+) are isolable in the solid state if combined with appropriate counteranions.     

Low-N lines of the A6sigma+-X6sigma+ (1,0) band of CrH

The (1,0) band of the A6sigma+-X6sigma+ electronic transition of CrH has been observed by laser-induced fluorescence following the reaction of laser-ablated Cr atoms with methanol under supersonic free-jet cooled conditions. Rotational assignments of the levels with N < or = 3 have been made by combination differences and dispersed fluorescence experiments on selected lines. These assignments complement those made from previously-recorded Fourier transform emission spectra, in which higher-N lines were assigned. The low-N rotational levels are extensively perturbed, presumably by levels of the a4sigma+, upsilon = 1 and B6pi, upsilon = 0 states.     

Radiative association of He+ with H2 at temperatures below 100 K

The paper presents a theoretical study of the low-energy dynamics of radiative association processes in the He+ + H2 collision system. Formation of the triatomic HeH2(+) ion in its bound rotation-vibration states on the potential-energy surfaces of the ground and of the first excited electronic states is investigated. Close-coupling calculations are performed to determine detailed state-to-state characteristics (bound <-- free transition rates, radiative and dissociative widths of resonances) as well as temperature-average characteristics (rate constants, photon emission spectra) of the two-state (X <-- A) reaction He+(2S) + H2(X1sigma(g)+) --> HeH2(+)(X2A') + h nu and of the single-state (A <-- A) reaction He+(2S) + H2(X1sigma(g)+) --> HeH2(+)(A2A') + h nu. The potential-energy surfaces of the X- and A-electronic states of HeH2(+) and the dipole moment surfaces determined ab initio in an earlier work [Kraemer, Spirko, and Bludsky, Chem. Phys. 276, 225 (2002)] are used in the calculations. The rate constants k(T) as functions of temperature are calculated for the temperature interval 1 < or = T < or = 100 K. The maximum k(T) values are predicted as 3.3 x 10(-15) s(-1) cm3 for the X <-- A reaction and 2.3 x 10(-20) s(-1) cm3 for the A <-- A reaction at temperatures around 2 K. Rotationally predissociating states of the He+-H2 complex, correlating with the upsilon = 0, j = 2 state of free H2, are found to play a crucial role in the dynamics of the association reactions at low temperatures; their contribution to the k(T) function of the X <-- A reaction at T < 30 K is estimated as larger than 80%. The calculated partial rate constants and emission spectra show that in the X <-- A reaction the HeH2(+)(X) ion is formed in its highly excited vibrational states. This is in contrast with the vibrational state population of the ion when formed via the (X <-- X) reaction He(1S) + H2(+)(X2sigma(g)+) --> HeH2(+)(X2A') + h nu.     

Experimental evidence for the curve crossing mechanism for collisional excitation in keV N2+*/He collisions by emission spectroscopy

Collision-induced emission (CIE) experiments were carried out by coupling a spectrograph and charge-coupled device detector (CCD) to a commercial analytical mass spectrometer. An Einzel lens and a deceleration-reacceleration lens assembly as described in the current article were installed in the mass spectrometer to allow for the deceleration of the ions before collision. Collision-induced emission spectra of N2+*/He collisions at lab frame collision energies from 2 to 8 keV were obtained from 190-1020 nm. The emissions were assigned to the Deltav=+2, +1, 0, -1, -2 vibrational transition progression in the N2+* B 2Sigmau+-->X 2Sigmag+ electronic transition as well as some atomic lines from the fragments N+, N* and the target gas He. N2+* A 2u-->X 2Sigmag+ emission was also observed but was very weak due to the long lifetime of the A 2u state. The relative intensities of the N2+*, N, and N+ emissions are independent of the ion translational energy within the studied energy range. This observation supports the curve-crossing mechanism for collisional excitation, suggesting that a complicated sequence of curve-crossings takes place upon collisional activation.     

Potential surfaces and dynamics of the O(3P)+H2O(X1A1)-->OH(X2pi)+OH(X2pi) reaction

We present global potential energy surfaces for the three lowest triplet states in O(3P)+H2O(X1A1) collisions and present results of classical dynamics calculations on the O(3P)+H2O(X1A1)-->OH(X2pi)+OH(X2pi) reaction using these surfaces. The surfaces are spline-based fits of approximately 20,000 fixed geometry ab initio calculations at the complete-active-space self-consistent field+second-order perturbation theory (CASSCF+MP2) level with a O(4s3p2d1f)/H(3s2p) one electron basis set. Computed rate constants compare well to measurements in the 1000-2500 K range using these surfaces. We also compute the total, rovibrationally resolved, and differential angular cross sections at fixed collision velocities from near threshold at approximately 4 km s(-1) (16.9 kcal mol(-1) collision energy) to 11 km s(-1) (122.5 kcal mol(-1) collision energy), and we compare these computed cross sections to available space-based and laboratory data. A major finding of the present work is that above approximately 40 kcal mol(-1) collision energy rovibrationally excited OH(X2pi) products are a significant and perhaps dominant contributor to the observed 1-5 micro spectral emission from O(3P)+H2O(X1A1) collisions. Another important result is that OH(X2pi) products are formed in two distinct rovibrational distributions. The "active" OH products are formed with the reagent O atom, and their rovibrational distributions are extremely hot. The remaining "spectator" OH is relatively rovibrationally cold. For the active OH, rotational energy is dominant at all collision velocities, but the opposite holds for the spectator OH. Summed over both OH products, below approximately 50 kcal mol(-1) collision energy, vibration dominates the OH internal energy, and above approximately 50 kcal mol(-1) rotation is greater than vibrational energy. As the collision energy increases, energy is diverted from vibration to mostly translational energy. We note that the present fitted surfaces can also be used to investigate direct collisional excitation of H2O(X1A1) by O(3P) and also OH(X2pi)+OH(X2pi) collisions.     

Structural and spectroscopic characterization of copper(II) complexes of a new bisamide functionalized imidazole tripod and evidence for the formation of a mononuclear end-on Cu-OOH species

A new polyimidazole tripod N,N-bis((1-methyl-4-pivalamidoimidazol-2-yl)methyl)-N'-((1-methylimidazol-2-yl)methyl)amine (L2) has been synthesized and shown to form intramolecular hydrogen bonds with different axial ligands bonded to Cu(II) in the solid state. The same hydrogen-bonding property of L2 appears responsible for the stabilization of a Cu(II)-OOH species in solution. The crystal structures of L2 and three of its Cu(II) complexes are reported. The [Cu(L2)X]ClO4 complexes, 4-6 (X- = Cl-, OH-, or N3-) have distorted trigonal bipyramidal geometries in the solid state and have been characterized further by UV-vis absorption, electron paramagnetic resonance (EPR) spectroscopy, and cyclic voltammetry. The reaction of [Cu(L2)OH](ClO4) (5) with H2O2 and tert-butyl hydroperoxide in methanol generates [Cu(L2)OOH](ClO4) (7) and [Cu(L2)OO(t)Bu](ClO4) (8) which have been characterized by different spectroscopic methods. The compound [Cu(L2)OO(t)Bu]+ displays a band at 395 nm (epsilon = 950 M(-1) cm(-1)) assigned to an alkylperoxo pi*(sigma) --> Cu ligand-to-metal charge transfer (LMCT) transition, while [Cu(L2)OOH]+ displays a peroxo pi*(sigma) --> Cu charge-transfer transition at 365 nm with epsilon = 1300 M(-1) cm(-1), a mass ion at m/z 593.4, and nu(O-O) stretch (resonance Raman) at 854 cm(-1) that shifts to lower energy by 46 cm(-1) upon 18O substitution.     

Time-dependent quantum wave-packet description of the 1pi sigma* photochemistry of phenol

The photoinduced hydrogen elimination reaction in phenol via the conical intersections of the dissociative 1pi sigma* state with the 1pi pi* state and the electronic ground state has been investigated by time-dependent quantum wave-packet calculations. A model including three intersecting electronic potential-energy surfaces (S0, 1pi sigma*, and 1pi pi*) and two nuclear degrees of freedom (OH stretching and OH torsion) has been constructed on the basis of accurate ab initio multireference electronic-structure data. The electronic population transfer processes at the conical intersections, the branching ratio between the two dissociation channels, and their dependence on the initial vibrational levels have been investigated by photoexciting phenol from different vibrational levels of its ground electronic state. The nonadiabatic transitions between the excited states and the ground state occur on a time scale of a few tens of femtoseconds if the 1pi pi*-1pi sigma* conical intersection is directly accessible, which requires the excitation of at least one quantum of the OH stretching mode in the 1pi pi* state. It is shown that the node structure, which is imposed on the nuclear wave packet by the initial preparation as well as by the transition through the first conical intersection (1pi pi*-1pi sigma*), has a profound effect on the nonadiabatic dynamics at the second conical intersection (1pi sigma*-S0). These findings suggest that laser control of the photodissociation of phenol via IR mode-specific excitation of vibrational levels in the electronic ground state should be possible.     

Optical study of diffuse bi-directional nanosecond pulsed dielectric barrier discharge in nitrogen

In this study, a bi-directional high voltage pulse with 20 ns rising time is employed to generate diffuse glow-like dielectric barrier discharge plasma with very low gas temperature in N2 using needle-plate electrode configuration at atmospheric pressure. Both the diffuse nanosecond pulsed dielectric barrier discharge images and the optical emission spectra of the discharge are recorded successfully under severe electromagnetic interference. The effects of pulse peak voltage, pulse repetition rate, and the concentrations of Ar and O2 on the emission intensities of NO (A2Σ→X2Π), OH (A2Σ→X2Π, 0-0), N2 (C3Πu→B3Πg, 0-0, 337.1 nm), and N2+ (B2Σu+→X2Σg+, 0-0, 391.4 nm) are investigated. The effects of the concentrations of Ar and O2 on the discharge diffuse performance are also studied. It is found that the emission intensities of NO (A2Σ→X2Π), OH (A2Σ→X2Π, 0-0), N2 (C3Πu→B3Πg, 0-0, 337.1 nm), and N2+ (B2Σu+→X2Σg+, 0-0, 391.4 nm) rise with increasing pulse peak voltage, pulse repetition rate, and the concentration of Ar, but decrease with increasing the concentration of O2. The main physicochemical processes involved are also discussed.     

Manifestation of stereoelectronic effects on the calculated carbon-hydrogen bond lengths and one bond (1)J(C-H) NMR coupling constants in cyclohexane,six-membered heterocycles,and cyclohexanone derivatives

Cyclohexane (1), oxygen-, sulfur-, and/or nitrogen-containing six-membered heterocycles 2-5, cyclohexanone (6), and cyclohexanone derivatives 7-16 were studied theoretically [B3LYP/6-31G(d,p) and PP/IGLO-III//B3LYP/6-31G(d,p) methods] to determine the structural (in particular C-H bond distances) and spectroscopic (specifically, one bond (1)J(C-H) NMR coupling constants) consequences of stereoelectronic hyperconjugative effects. The results confirm the importance of n(X) --> sigma*(C-H)(app) (where X = O, N), sigma(C-H)(ax) --> pi*(C=O), sigma(S-C) --> sigma*(C-H)(app), sigma(C-S)-->sigma*(C-H)(app), beta-n(O) --> sigma*(C-H), and sigma(C-H) --> sigma*(C-H)(app) hyperconjugation, as advanced in previous theoretical models. Calculated r(C-H) bond lengths and (1)J(C-H) coupling constants for C-H bonds participating in more than one hyperconjugative interaction show additivity of the effects.     

cis-Dicyanoosmium(II) diimine complexes bearing phosphine or sulfoxide ligands: spectroscopic and luminescent studies

A series of cis-dicyanoosmium(II) complexes [Os(PPh3)2(CN)2(N intersectionN)] (N intersectionN = Ph2phen (2a), bpy (2b), phen (2c), Ph2bpy (2d), tBu2bpy (2e)) and [Os(DMSO)2(CN)2(N intersectionN)] (3a-3e, N intersectionN = Br2phen (3f), Clphen (3g)), were synthesized and their spectroscopic and photophysical properties were examined, and [Os(PMe3)2(CN)2(phen)] (4) with axial PMe3 ligands was similarly prepared. The molecular structures of 2a, 2c, [2c.Zn(NO3)2]infinity, 2d, 2e, 3b, 3d, 3e, and 4 were determined by X-ray crystallographic analyses. The two CN ligands are cis to each other with mean Os-C bond distance of 2.0 A. The two PR3 (R = Ph, Me) or DMSO ligands are trans to each other with P/S-Os-P/S angles of approximately 177 degrees . The UV-vis absorption spectra of 2a-2e display an intense absorption band at 268-315 nm (epsilon = approximately (1.54-4.82) x 104 M-1 cm-1) that are attributed to pi --> pi*(N intersection N) and/or pi --> pi*(PPh3) transitions. The moderately intense absorption bands with lambdamax at 387-460 nm (epsilon = approximately (2.4-11.3) x 103 M(-1) cm(-1)) are attributed to a 1MLCT transition. A weak, broad absorption at 487-600 nm (epsilon = approximately 390-1900 M(-1) cm(-1)) is assigned to a 3MLCT transition. Excitation of 2a-2e in dichloromethane at 420 nm gives an emission with peak maximum at 654-703 nm and lifetime of 0.16-0.67 micros. The emission energies, lifetimes, and quantum yields show solvatochromic responses, and plots of numax, tau, and Phi, respectively, versus ET (solvent polarity parameter) show linear correlations, indicating that the emission is sensitive to the local environment. The broad structureless solid-state emission of 2a-2e at 298 (lambdamax 622-707 nm) and 77 (lambdamax 602-675 nm) K are assigned to 3MLCT excited states. The 77 K MeOH/EtOH (1:4) glassy solutions of 2a-2e also exhibit 3MLCT emissions with lambdamax = 560-585 nm. The 1MLCT absorption and 3MLCT emission of 3a-3g occur at lambdamax = 332-390 nm and 553-644 nm, respectively. In the presence of Zn(NO3)2, both the 1MLCT absorption and 3MLCT emission of 2c in acetonitrile blue-shift from 397 to 341 nm and 651 to 531 nm, respectively. The enhancement of emission intensity (I/Io) of 2e at 531 nm reached a maximum of approximately 810 upon the addition of two equivs of Zn(NO3)2. The crystallographic and spectroscopic evidence suggests that 2c undergoes binding of Zn2+ ions via the cyano moieties.