Ionization Energy IE Research Articles

On the Effect of Donor Strength on the Photoluminescence Performance in Mono‐Substituted N‐Donor Triarylmethyl Radicals

AbstractThe functionalization of light‐emitting triarylmethyl radicals with electron‐donating moieties can significantly increase their photoluminescence quantum yield ϕ. As luminophores in light‐emitting diodes, such open‐shell radicals can be used to overcome the problem of spin‐statistics inherent to conventional closed‐shell emitters. However, so far the functionalization of triarylmethyl radicals with donors of varying strength is limited by the restricted reactivity of the triarylmethyl radical, constraining optimization of performance to empirical trial and error approaches. Here, the reliable reactivity of N‐heterocyclic donors is used in radical‐mediated aromatic substitutions, allowing to systematically investigate the effect of donor strength on the emission characteristics of triarylmethyl radicals. As a single descriptor proxy to the donor strength, the ionization energy IE of the donor moiety is employed, which is determined by density functional theory calculations. A systematic bathochromic shift of the emission wavelength λmax is observed for increasing donor strength, while maximum ϕ values are obtained for medium‐strength donors. These effects are rationalized with a simple model based on Marcus theory supported by quantum chemical calculations and electron paramagnetic resonance. This allows to understand the effect of the donor strength on both λmax and ϕ, enabling the design of improved light‐emitting radicals in the future.

Theoretical dissociation, ionization, and spin-orbit energetics of the diatomic platinum hydrides PtH, PtH+, and PtH.

Spin-orbit configuration interaction (SO-CI) and coupled-cluster [CCSDT(Q)] theoretical methods are combined to evaluate zero-temperature thermochemical properties of PtH, PtH+, and PtH-. We obtain vibrational zero-point energies and spin-orbit stabilization energies, which lead to predictions for observable quantities: ionization energy IE(PtH) = (9.44 ± 0.07) eV; electron affinity EA(PtH) = (1.65 ± 0.04) eV; and dissociation energies D0(Pt-H) = (329.6 ± 3.9) kJ mol-1, D0(Pt+-H) = (279.3 ± 5.7) kJ mol-1, and D0(Pt--H) = (285.0 ± 2.4) kJ mol-1 (uncertainty coverage factor = 2). Compared with available experiments, our value of D0(Pt+-H) is higher by (8 ± 8) kJ mol-1, EA(PtH) is higher by 0.15eV, and D0(Pt-H) is lower than the upper bound by (2 ± 4) kJ mol-1.

Electronic structure and thermochemistry for monocarbides MC, MC+ and MC− (M=Zn, Cd, Hg): CCSD(T) and DFT works

In this work, the ab-initio coupled cluster CCSD(T) method and the B3LYP, BP91W and CAM-B3LYP functional of DFT method in conjunction with the aug-cc-pVTZ-PP basis have been applied to study the group 12 monocarbides MC, MC+ and MC−. The potential energy curves (PECs) for the three electronic states 3Σ−, 5Σ− and 1Δ of the MC and the two states 2∑- and 4∑- for the MC+ cations and MC− anions have been investigated. In addition, Bond distance Re, transition energy Te, vibrational frequency ωe, ionization energy IE, electron affinity EA, dipole moment μ, dissociation energy D0 and heat formation ΔH°f0/ΔH°f298, were determined for each species. The analysis of the dissociation energy for ZnC, CdC and HgC shows the decrease in the stability of the monocarbides from Zn to Hg. For ΔH°f0/ΔH°f298 values of MC, which are not known experimentally or theoretically, we recommend the following CCSD(T) predictions of ZnC, CdC and HgC: 181.3/178.54, 180.65/178.4 and 175.35/174.71 kcal/mol respectively. Comparing the three functionals with the CCSD(T) results, the CAM-B3LYP functional shows excellent predictive agreement for the various properties of the group 12 monocarbides.

Vibrational spectroscopic investigation of the gold complexation within the cascade structure of phosphorus-containing dendrimer

The interaction of the phosphoric dendrimer with gold was performed by means of vibrational spectroscopy and quantum chemistry. Stable complexes are formed with a PN−PS linkage, whereas with an isolated PS bond this does not occur.The change in geometric parameters and delocalization of electric charge under the influence of gold was discovered. The classification of bands in the experimental vibrational spectra of the dendrimer and its complex was carried out.HOMO of molecule of the dendrimer is localized on the SPNP linkage, whereas the LUMO is located on the terminal group. In the SPNP linkage there is a noticeable delocalization of the charge which leads to a change in the reactivity of this group. Interaction energy was estimated as the difference between the energies of the complex and the energies of the molecules of the dendrimer G′0 and two molecules AuCl and is equal to 25.2 eV. The ionization energy IE and electron affinity EA for AuCl are higher than for dendrimer, therefore, when the complex is formed, these quantities increases. Chemical potential and the electrophilicity index in the complex also increases.

Bond Dissociation Energies of Tungsten Molecules: WC, WSi, WS, WSe, and WCl.

Resonant two-photon ionization spectroscopy was used to locate predissociation thresholds in WC, WSi, WS, WSe, and WCl, allowing bond dissociation energies to be measured for these species. Because of the high degree of vibronic congestion in the observed spectra, it is thought that the molecules dissociate as soon as the lowest separated atom limit is exceeded. From the observed predissociation thresholds, dissociation energies are assigned as D0(WC) = 5.289(8) eV, D0(WSi) = 3.103(10) eV, D0(WS) = 4.935(3) eV, D0(WSe) = 4.333(6) eV, and D0(WCl) = 3.818(6) eV. These results are combined with other data to obtain the ionization energy IE(WC) = 8.39(9) eV and the anionic bond dissociation energies of D0(W-C-) = 6.181(17) eV, D0(W--C) = 7.363(19) eV, D0(W-Si-) ≤ 3.44(4) eV, and D0(W--Si) ≤ 4.01(4) eV. Combination of the D0(WX) values with atomic enthalpies of formation also provides ΔfH0K° values for the gaseous WX molecules. Computational results are also provided, which shed some light on the electronic structure of these molecules.

H2CN+ and H2CNH+: New insight into the structure and dynamics from mass-selected threshold photoelectron spectra

In this paper, we reinvestigate the photoionization of nitrogen containing reactive intermediates of the composition H2CN and H2CNH, molecules of importance in astrochemistry and biofuel combustion. In particular, H2CN is also of considerable interest to theory, because of its complicated potential energy surface. The species were generated by flash pyrolysis, ionized with vacuum ultraviolet synchrotron radiation, and studied by mass-selected threshold photoelectron (TPE) spectroscopy. In the mass-selected TPE-spectrum of m/z = 28, contributions of all four isomers of H2CN were identified. The excitation energy to the triplet cation of the methylene amidogen radical H2CN was determined to be 12.32 eV. Considerable activity in the C-N mode of the cation is visible. Furthermore, we derived values for excitation into the triplet cations of 11.72 eV for cis-HCNH, 12.65 eV for trans-HCNH, and 11.21 eV for H2NC. The latter values are probably accurate to within one vibrational quantum. The spectrum features an additional peak at 10.43 eV that corresponds to excitation into the C(2v)-symmetric H2CN(+). As this structure constitutes a saddle point, the peak is assigned to an activated complex on the singlet potential energy surface of the cation, corresponding to a hydrogen atom migration. For methanimine, H2CNH, the adiabatic ionization energy IE(ad) was determined to be 9.99 eV and the vibrational structure of the spectrum was analyzed in detail. The uncertainty of earlier values that simply assigned the signal onset to the IE(ad) is thus considerably reduced. The spectrum is dominated by the H-N-C bending mode ν1(+) and the rocking mode ν3(+). All experimental data were supported by calculations and Franck-Condon simulations.

Comprehensive vacuum ultraviolet photoionization study of the CF3• trifluoromethyl radical using synchrotron radiation

The trifluoromethyl radical, CF(3)(●), is studied for the first time by means of threshold photoelectron spectroscopy (TPES). The radical is produced in the gas phase using the flash-pyrolysis technique from hexafluoroethane as a precursor. CF(3)(+) total ion yield and mass-selected TPES of the radical are recorded using a spectrometer based upon velocity map imaging and Wiley-McLaren time-of-flight coupled to the synchrotron radiation. The high resolution of the instrument and of the photons allows the observation of rich vibrational progressions in the TPES of CF(3)(●). By using Franck-Condon factors computed by Bowman and coworkers, we have been able to simulate the TPES. The initial vibrational temperature of the radical beam has been evaluated at 350 ± 70 K. The structures have been identified as transitions between (n(1),n(2)) and (n(1)(+),n(2)(+)) vibrational levels of CF(3) and CF(3)(+) with small excitation of the breathing mode, ν(1)(+) (,) and large excitation (n(2)(+) = 10-26) of the umbrella mode, ν(2)(+), in the cation. From the energy separation between the two resolved peaks of each band, a value of 994 ± 16 cm(-1) has been derived for the ν(1)(+) breathing frequency of CF(3)(+). For the high-lying n(2)(+) levels, the apparent ν(2)(+) umbrella spacing, 820 ± 14 cm(-1), is fairly constant. Taking into account the ν(2)(+) anharmonicity calculated by Bowman and coworkers, we have deduced ν(2)(+) = 809 ± 14 cm(-1), and semi-empirical estimations of the adiabatic ionization energy IE(ad.)(CF(3)(●)) are proposed in good agreement with most of previous works. A value of the vertical ionization potential, IE(vert.)(CF(3)(●)) = 11.02 eV, has been derived from the observation of a photoelectron spectrum recorded at a fixed photon energy of 12 eV.

Threshold Photoelectron Spectroscopy of Cyclopropenylidene, Chlorocyclopropenylidene, and Their Deuterated Isotopomeres

Cyclopropenylidene (c-C(3)H(2)), chlorocyclopropenylidene (c-C(3)HCl), and their deuterated isotopomers were studied by the threshold photoelectron-photoion coincidence (TPEPICO) technique using VUV synchrotron radiation. The carbenes were generated via flash pyrolysis. In all species a change in geometry is visible upon ionization, with significant activity in the C═C, C-C-stretching mode and, in the case of c-C(3)H(2)/D(2), the C-H-bending mode. The electron is removed from an sp(2) like hybrid orbital centered on the carbene C atom. The mass selected threshold photoelectron (TPE) spectra were fitted by a Franck-Condon simulation, yielding the equilibrium geometry of the cation ground state ((1)A(1)). The adiabatic ionization energy IE(ad) of c-C(3)H(2) was determined to be 9.17 eV, in good agreement with calculations and literature values. Two vibrational wavenumbers of the cation were determined experimentally (ν(3)(+) = 1150 cm(-1) and ν(2)(+) = 1530 cm(-1)). Chlorocyclopropenylidene was also studied by TPE spectroscopy and has a similar IE(ad) of 9.17 eV. The spectrum also shows a vibrational progression that corresponds to the C═C- and C-C-stretching modes of the cation. The equilibrium geometry was also determined by a Franck-Condon fit. The IE(ad) of the deuterated isotopomers, c-C(3)D(2) and c-C(3)DCl, were also determined to be 9.17 eV. The spectra confirm the assignments for the nondeuterated species.

DFT calculations of structure and vibrational spectra of dendron built of cyclotriphosphazene core with terminal carbamate and ester groups

FTIR and FT-Raman spectra of dendron built of the cyclotriphosphazene core with five carbamate and one ester functions ( G 0) and [2-(4-hydroxyphenyl)ethyl]-carbamic acid tert-butyl ester ( C) have been recorded at various temperatures between 16 and 70 °C. The bands of free ν(N–H) and ν(C O) bonds are not observed in the IR spectra of C in the crystalline state and in the melt, and thus association of carbamate groups by hydrogen bonds occur. The frequencies of ν(N–H) and ν(C O) bands in the IR spectra reveal the presence of the different types of H-bonds in the amorphous state of G 0. Density functional theory (DFT) calculations of C gave vibrational frequencies and intensity of IR bands for the t-g-, g-g-, tg-, gg-conformers. The most stable is the gg-conformer. The bond lengths, bond angles, frequencies and intensity of bands in the IR spectra of dendron obtained by DFT show the best agreement with experimental data. Relying on DFT calculations a complete assignment of vibrations is proposed for different parts of dendron. The ionization energy IE, electron affinity EA and global softness of G 0 are higher than that of C. The most reactive places in C are OH, NH and C O groups. The local softness of C O bond of carbamate group in G 0 for nucleophilic attack is lower than that of methylbenzoate group.

Electronic states of BP, BP +, BP −, B 2P 2, [formula omitted] and [formula omitted

Using augmented sextuple zeta basis sets and internally contracted multireference configuration interaction (MRCI) wavefunctions, potential energy, electric dipole and transition moments have been computed for the X 3Π, a 1Σ +, b 1Π and A 3Σ − states of BP, X 2Σ + and A 2Π states of BP − and X 4Σ − and A 4Π states of BP +. From these data spectroscopic constants, radiative transition probabilities and photoelectron spectra of BP − and BP have been evaluated. The non-vanishing spin–orbit coupling elements between the four low lying triplet and singlet states of the neutral BP have also been calculated from MRCI wavefunctions. The treatment of the corresponding perturbations in the manifold of dense rovibrational states in the three lowest states would require a precise knowledge of the electronic excitation energies. Our best singlet–triplet separations (X–a) are calculated to be 2412 cm −1 (MRCI) and 2482 cm −1 (restricted coupled cluster with perturbative triples (RCCSD(T))) with an estimated error bound of about ±200 cm −1. All three states have long radiative lifetimes with cascading among the rovibrational levels of different states. The ionization energy IE e of BP is calculated to be 9.22 eV (MRCI) and 9.48 eV (RCCSD(T)), the electron affinity EA e 2.51 eV (MRCI) and 2.74 eV (RCCSD(T)). The photoelectron spectra of BP and BP − have been obtained from the Franck–Condon factors of the MRCI potentials. For the UV spectroscopy the dipole allowed radiative transition probabilities are given for A 3Σ − ↔ X 3Π, b 1Π ↔ a 1Σ + of BP, A 2Π ↔ X 2Σ + of BP − and A 4Π ↔ X 4Σ − of BP +. The ionization energy IE e of B 2P 2 of 8.71 eV and the electron affinity EA e of 2.34 eV have been calculated by the RCCSD(T)/aVQZ approach. Also the harmonic vibrational wavenumbers for the electronic ground states of the ions B 2 P 2 + and B 2 P 2 - are given.

Revision of the second ionization energy of toluene

Charge stripping (CS) of the molecular ion of toluene, C(7)H(8) (+)-->C(7)H(8) (2+)+e, is often used as a reference for the determination of second ionization energies in energy-resolved CS experiments. For calibration of the kinetic energy scale, a value of IE(C(7)H(8) (+))=(15.7+/-0.2) eV derived from the appearance energy of the toluene dication upon electron ionization has been accepted generally. Triggered by some recent discrepancies between CS measurements on the one hand and different experimental methods as well as theoretical predictions on the other, we have reinvestigated the photon-induced double ionization of toluene using synchrotron radiation. These photoionization measurements yield phenomenological appearance energies of AE(C(7)H(8) (+))=(8.81+/-0.03) eV for the monocation and AE(C(7)H(8) (2+))=(23.81+/-0.06) eV for the dication. The former is in good agreement with a much more precise spectroscopic value, IE(C(7)H(8))=(8.8276+/-0.0006) eV. Explicit consideration of the Franck-Condon envelopes associated with photoionization to the dication in conjunction with the application of the Wannier law leads to an adiabatic ionization energy IE(a)(C(7)H(8) (+))=(14.8+/-0.1) eV, which is as much as 0.9 eV lower than the previous value derived from electron ionization. Because in many previous CS measurements the transition C(7)H(8) (+)-->C(7)H(8) (2+)+e was used as a reference, the energetics of several gaseous dications might need some readjustment.

Ab initio studies on the electronic structure of FeOH

The electronic structure of FeOH has been studied by using the all-electron multireference averaged coupled-pair functional (ACPF) method combined with the scalar-relativistic Douglas–Kroll–Heβ (DKH) Hamiltonian. A linear geometry (ground state 6Δ, RFe–O = 1.7501 Å, RO–H = 0.9444 Å) is found to be the most stable structure for FeOH. Relativistic effects must be taken into account in order to predict the correct ground state. Furthermore, inner-shell correlation effects are also important for the Fe–O bond of FeOH, i.e., the Fe–O distance is lengthened by at least 0.02 Å when the iron 3s and 3p orbitals are frozen at the ACPF level. The calculated ionization energy IE (7.43 eV) and standard gas phase enthalpies of formation ΔHf0 (21.03 kcal/mol) are in good agreement with Gorokhov’s measurement (IE: 7.6 ± 0.3 eV, ΔHf0 : 25.4 ± 4.1 kcal/mol). The obtained Fe–OH dissociation energy D0 (3.61 eV) agrees well with the recent experimental value 3.50 ± 0.12 eV obtained by Schröder and Schwarz but exceeds the error bar of Murad’s older measurement (3.33 ± 0.17 eV ) by 0.13 eV.

Thermochemistry of small cationic iron–sulfur clusters

The kinetic energy dependences of the reactions of Fen+ with COS (n=2–6) and CS2 (n=2–5) are studied in a guided-ion beam tandem mass-spectrometer. The main products arise from sulfur transfer and subsequent losses of Fe atoms. In the case of CS2, this reactant also formally replaces one Fe atom of the cluster to form Fen−1CS2+ with losses of further Fe atoms at elevated energies. In addition, the kinetic energy dependences of the reactions of FenS+ (n=2–4) with Xe and CS2 are studied. The former system yields collision-induced dissociations, whereas the latter reagent effects sulfur transfer accompanied by subsequent losses of Fe atoms. Analyses of the cross sections for endothermic reactions yield the bond energies D0(Fen+–S), n=2–5, D0(SFen−1+–Fe), n=2–5, D0(SFen+−S), n=1–3, and D0(S2Fen−1+–Fe), n=2, 3, as well as the ionization energy IE(Fe2S2). These values are derived with explicit consideration of the lifetimes of the energized reaction intermediates. The binding between sulfur and the cluster core strengthens as the cluster size increases, which is rationalized by simple structural arguments.

On the Enthalpy of Formation of Hydroxyl Radical and Gas-Phase Bond Dissociation Energies of Water and Hydroxyl

In a recent letter (J. Phys. Chem. A, 2001, 105,1), we argued that, although all major thermochemical tables recommend a value of (OH) based on a spectroscopic approach, the correct value is 0.5 kcal/mol lower as determined from an ion cycle. In this paper, we expand upon and augment both the experimental and theoretical arguments presented in the letter. In particular, three separate experiments (mass-selected photoionization measurements, pulsed-field-ionization photoelectron spectroscopy measurements, and photoelectron-photoion coincidence measurements) utilizing the positive ion cycle to derive the O−H bond energy are shown to converge to a consensus value of the appearance energy AE0(OH+/H2O) = 146117 ± 24 cm-1 (18.1162 ± 0.0030 eV). With the most accurate currently available zero kinetic energy photoionization value for the ionization energy IE(OH) = 104989 ± 2 cm-1, corroborated by a number of photoelectron measurements, this leads to D0(H−OH) = 41128 ± 24 cm-1 = 117.59 ± 0.07 kcal/mol. This corres...

Chemical kinetics of lanthanum ionization in H 2–O 2–N 2 flames

Trace amounts (≤10 −6 mol fraction) of lanthanum were introduced into five, premixed, fuel-rich, H 2–O 2–N 2 flames at atmospheric pressure in the temperature range 1820–2400 K. Aqueous salt solutions of the metal were sprayed into the premixed flame gas as an aerosol using an atomizer technique. The concentrations of the major neutral species present in flames, believed to be LaO and OLaOH, are linked by the balanced reaction LaO + H 2O = OLaOH + H having an equilibrium constant K = 0.1859 exp(−11 464/ T), based on a crude estimate of the bond dissociation energy for lanthanum oxide-hydroxide D 0 0(OLa–OH) = 408 ± 40 kJ mol −1. Metallic ions were observed by sampling the flames through a nozzle into a mass spectrometer and, for kinetics purposes, were measured as profiles of ion concentration versus distance (i.e. time) along the flame axis. The ions detected can be represented by an oxide ion series LaO +. nH 2O ( n = 0−3 or more); the genuine flame ions are thought to be LaO + ( n = 0) and La(OH) 2 + ( n = 1), equivalent to protonated OLaOH. The two ions are linked by the fast balanced reaction LaO + + H 2O + M = La(OH) 2 + + M, where M is a third body. The major ion production processes appear to be the chem-ionization reaction OLaOH + H ⇄ La(OH) 2 + + e −, and thermal (collisional) ionization LaO + M ⇄ LaO + + e − + M because the ionization energy IE 0 0(LaO) = 4.90 eV is low. Ion loss processes involve dissociative electron–ion recombination. When electron-ion recombination of LaO +. nH 2O was made dominant by the trace addition of potassium, values of the global recombination coefficient are given by (1718 ± 515) T −3.0±0.2 cm 3 molecule −1 s −1. The rate constant for thermal (collisional) ionization of LaO was found to be 8.0 × 10 −10 T 1/2 exp(−IE 0 0/RT) cm 3 molecule −1 s −1. The pre-exponential factor or cross section is only 8% of that determined for the alkali metals. The rate constant for the chemi-ionization of OLaOH is given by (5.6 ± 1.7) × 10 −12 exp(−17 350/ T) cm 3 molecule −1 s −1. Although no direct evidence was found for particle formation in these flames, both rate constants for ion production would be lower limits if appreciable lanthanum were present as solid particles.

Magnesium chemistry in the gas phase: calculated thermodynamic properties and experimental ion chemistry in H 2–O 2–N 2 flames

Molecular orbital calculations were carried out for the neutral and ionic species that occur in the gas-phase chemistry of magnesium in the presence of oxygen and hydrogen including Mg +, MgO, MgOH, MgOH +, MgOH 2 +, Mg(OH) 2, HOMgOH 2 +, and the hydrate structure MgOH + … (OH 2). Standard enthalpies of formation for these species were obtained from single-point calculations at the QCISD(T)(full)/6-311++G(2df,p) and CCSD(T)(full)/6-311++G(2df,p) levels of theory using geometrical parameters obtained from MP2(full)/6-311++G(d,p) optimizations. These Δ H f 0 values provide a recommended and self-consistent set with uncertainties as small as ±12.6 kJ mol −1 (±3 kcal mol −1) for deriving thermodynamic properties. The properties of interest include the proton affinities PA 298 0 of MgO, MgOH, and Mg(OH) 2, ionization energy IE 0 0 of MgOH, bond dissociation energies D 0 0 of Mg–O, Mg–OH, MgO–H, HOMg–OH, Mg–OH +, H 2O–Mg +, and H 2O–MgOH +; the latter two are hydration energies. Values in the literature, both experimental and theoretical, for many of these quantities show considerable scatter and a detailed comparison is made. Magnesium ions in fuel-rich, H 2–O 2–N 2 flames at atmospheric pressure in the temperature range 1820–2400 K were investigated experimentally by sampling the flames doped with magnesium through a nozzle into a mass spectrometer. It was shown that the interconversion of Mg + and MgOH + proceeds by way of the three-body reaction of Mg + with OH, in support of Sugden’s criterion that this occurs in flames if the weak HO–Mg + bond has a dissociation energy less than 335 kJ mol −1. The proton affinity PA 298 0(MgO) was measured to be 1056 ± 29 kJ mol −1 (252 ± 7 kcal mol −1) along with approximate values for PA 298 0(MgOH) = 919 kJ mol −1 (220 kcal mol −1) and PA 298 0[Mg(OH) 2] = 878 kJ mol −1 (210 kcal mol −1). Values were estimated for the electron–ion recombination coefficient for MgH m O n + molecular ions of 2 × 10 −7 cm 3 molecule −1 s −1, and for Mg + of 4 × 10 −24 T −1 cm 6 molecule −2 s −1 similar to those for alkali metal ions. Finally, small rate coefficients for the chemi-ionization of magnesium via the reactions of Mg + OH and MgO + H to give MgOH + were estimated to be 4.832 × 10 −9 exp(−55 700/ T) and 3.341 × 10 −9 exp(−32 970/ T) cm 3 molecule −1 s −1, respectively.

Some calculated properties of phenylphosphinidene (C 6H 5P)

Ab initio molecular orbital (MP2/6-311G(d,p) and CASPT2/ANO) and density functionl theory (DFT/IGLO-III) calculations have been applied to determine some basic properties of phenyl phosphinidenee (C 6H 5P). Geometrics, harmonic vibrational wavenumbers, singlet-triplet energy gaps, heats of formation and hyperfine splitting constants have been calculated. Phenylphosphinidene has a triplet 3A 2 ground state lying 22±3 kcal/mol below the closed-shell singlet 1A 1 state and some calculated properties are: heat of formation at 0 K ΔH 0 f,0 = 68 ± 5 kcal/mol, vertical ionization energy IE v = 10.6 ± 0.3 eV, electron affinity EA a = 0.89±03 eV, proton affinity PA = 140±5 kcal/mol and isotropic hyperfine splitting constant a( 31 P) = 66 ± 3 G . The open-shell singlet 1A 2 state is a low-lying state having comparable energy with the 1A 1. The properties of C 6H 5P are similar to those of methylphosphinidene (CH 3P). The singlet-triplet gap ( 1A′– 3A 2) in CH 3P amounts to 26 ± 3 kcal/mol. Relative to the CH 3P, the phneyl group has a small effect on the singlet state but seems to destabilize the triplet state and thereby reduce the singlet-triplet gap.

Experimental and theoretical study of the dissociation energies D0(H 2NH) and D0(H 2N +H) and other related quantities

Combining the techniques of molecular beam and vacuum ultraviolet synchrotron radiation photoionization mass spectroscopy, we have measured the ionization energy of NH 3 (10.16±0.02 eV) and the appearance potentials of H + (18.57±0.05 eV) and NH 2 + (15.75±0.02 eV). From these data, we have obtained dissociation energy values for D 0(H 2NH) (4.97±0.05 eV), D 0(H 2N +H) (5.59±0.02 eV) and D 0(H 2NH +) (8.41±0.05 eV) and the ionization energy IE(NH 2) (10.78±0.05 eV). High-level ab initio calculations lead to results that are in good agreement with the experimental findings.

Gas Phase UV Photoelectron Spectroscopy as a Tool for the Investigation of Electronic Structures of Coordination Compounds

Abstract Photoelectron spectroscopy is nothing but the application of the photoelectron effect to the study of the photoionization processes occurring in matter interacting with electromagnetic radiation. More precisely, photoelectronic spectroscopy deals with the measurement of the kinetic energy of the electrons emitted by matter owing to this interaction. When the matter is in the gas phase, and the light is of short wavelength, i.e. in the far ultraviolet, the entities involved in the photoionization are free molecules and the photoelectrons are ejected from the occupied molecular orbitals. The kinetic energy (KE) of a photoelectron ejected from the jth MO is given by the difference between the energy of the monochromatic radiation and the ionization energy corresponding to the removal of an electron from the jth MO: KE=hv − IE, (1.1) provided we disregard, as a first approximation, additional possibilities of vibrational or rotational excitation on ionization. Gas-phase UV photoelectron spectroscopy (UPS) is the study of the energies, abundances and angular distributions of photoelectrons. Knowledge of the ionization energies for the various molecular orbitals in a molecule is of fundamental importance in the study of molecular electronic structure. In fact, following an approximation known as Koopmans' theorem,1 each ionization energy IE, is equal in magnitude to the calculated SCF MO eigenvalue ey IE,=− ej, (1.2)

Charge stripping of ethane ions

Values for the vertical ionization energies of ions from ethane have been determined by charge stripping high-velocity ions with nitrogen collision gas and measuring the value of Q min, the minimum translational energy loss. The ionization energy IE (m + → m 2+) can be measured directly for processes in which the product m 2+ ions are sufficiently stable to reach the ion collector. This is the case for C 2H 5 2+·, C 2H 4 2+, C 2H 3 2+·, C 2H 2 2+ and C 2H 2+·. Ions C 2H 6 2+ are, however, unstable and fragment to give C 2H 5 2+· ions among the products. The translational energy of these product ions can be used to determine IE (C 2H 6 +· → C 2H 6 2+). Measurements were also obtained on all the singly-charged ions from pentadeuteroethane. In this case, the ion kinetic energy spectrum of C 2HD 5 +· showed a peak due to the process C 2HD 5 +· → (C 2HD 5 2+) → C 2HD 3 2+. The position of this peak enabled a value for IE (C 2HD 5 +· → C 2HD 5 2+) to be calculated. The values obtained from the pentadeutero compound confirmed those from ethane.