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The observation of molecular isomerization dynamics is a long-standing goal in physical chemistry. The loosely bound electron in a dipole-bound state (DBS) can be a messenger for probing the isomerization of the neutral core. Here we study the isomerization dynamics of the salt dimer (NaCl)

The tantalum anion has the most complicated photoelectron spectrum among all atomic anions of transition elements, which was the main obstacle to accurately measure its electron affinity via the generic method. The latest experimental value of the electron affinity of Ta was 0.323(12) eV, reported by Feigerle et al. [J. Chem. Phys. 74, 1580 (1981)]. In the present work, we report the high-resolution photoelectron spectroscopy of Ta− via the slow-electron velocity-map imaging method combined with a cryogenic ion trap. The electron affinity of Ta was measured to be 2652.38(17) cm−1 or 0.328 859(23) eV. Three excited states 5 D1, 3 P0, and 5 D2 of Ta− were observed, and their energy levels were determined to be 1169.64(17) cm−1 for 5 D1, 1735.9(10) cm−1 for 3 P0, and 2320.1(20) cm−1 for 5 D2 above the ground state 5 D0, respectively.

We report a high-resolution photoelectron imaging and photodetachment spectroscopy study of cryogenically cooled IO-. The high-resolution photoelectron spectra yield a more accurate electron affinity (EA) of 2.3805(5) eV for IO as well as a more accurate spin-orbit splitting energy between the 2Π3/2 and 2Π1/2 states of IO as 2093(5) cm-1. Photodetachment spectroscopy confirmed several excited states for the IO- anion predicted by theoretical calculations, including two valence-type excited states, the repulsive 3Π state, and a shallow bound 1Π state. More interestingly, we have observed two vibrational resonances which are proposed to be due to a dipole-induced resonant state, about 230 cm-1 above the detachment threshold of IO-.

The latest experimental electron affinity (EA) values of atomic scandium and yttrium were 0.189(20) and 0.308(12) eV as reported by Feigerle et al. in 1981. The measurement accuracy of these was far lower than that of other transition elements, and no conclusive result had been made on the excited states of their negative ions. In the current work, we report more accurate EA values of Sc and Y and the electronic structure of their negative ions using the slow-electron velocity-map imaging method. The EA values of Sc and Y are determined to be 0.179 378(22) and 0.311 29(22) eV, respectively. The ground state of Sc− is identified as 3 d4 s24 p 1 D2, and the ground state is 4 d5 s25 p 1 D2 for Y−. Furthermore, several excited states of Sc− and Y− are observed: Sc− (3 D1) and Y− (3 D1, 3 D2, 3 D3, 3 F2, and 3 F3), and their energy levels are determined to be 1131.8(28), 1210.0(13), 1362.3(30), 1467.7(26), 1747(16), and 1987(33) cm−1, respectively.

Electron affinities (EAs) of most lanthanide elements still remain unknown due to their relatively low EA values. In the present work, the cryogenically controlled ion trap is used for accumulating atomic lutetium anion Lu $^-$ , which makes the measurement of electron affinity of lutetium become practicable. The high-resolution photoelectron spectra of Lu $^-$ are obtained via the slow-electron velocity-map imaging method. The electron affinity of Lu is determined to be 1926.2(50) cm $^{-1}$ or 0.23882(62) eV. In addition, two excited states of Lu $^-$ are observed.

The electronic structures of actinide systems are extremely complicated because of strong electron correlations and relativistic effects. The atomic actinide anion poses even more challenges for experimental and theoretical investigations due to the extra loosely bound electron. In this work, we report the electronic structure of ${\mathrm{U}}^{\ensuremath{-}}$ using the slow-electron velocity-map imaging method. The electron affinity of U was measured to be 314.97(9) meV. Two excited states of ${\mathrm{U}}^{\ensuremath{-}}$ were observed and their energies were determined to be 84(11) and 160(12) meV above its ground state, respectively. The present study provides convincing evidence that the transition between the first excited state and the ground state of ${\mathrm{U}}^{\ensuremath{-}}$ is electric dipole (E1) allowed.

Despite the fact that the laser-cooling method is a well-established technique to obtain ultracold neutral atoms and atomic cations, it has rarely if ever been applied to atomic anions due to the lack of suitable electric-dipole transitions. Efforts of more than a decade have until recently only resulted in ${\mathrm{La}}^{\ensuremath{-}}$ as a promising anion candidate for laser cooling, but our previous work [Tang et al., Phys. Rev. Lett. 123, 203002 (2019)] showed that ${\mathrm{Th}}^{\ensuremath{-}}$ is also a potential candidate. Here we report on a combination of experimental and theoretical studies to determine the frequencies and rates, as well as branching ratios, for the relevant transitions in ${\mathrm{Th}}^{\ensuremath{-}}$. The resonant frequency of the laser-cooling transition is determined to be $\ensuremath{\nu}=123.455(30)$ THz $[\ensuremath{\lambda}=2428.4(6)\phantom{\rule{0.16em}{0ex}}\mathrm{nm}]$. The transition rate is calculated as $A=1.17\ifmmode\times\else\texttimes\fi{}{10}^{4}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. Since the branching fraction to dark states is negligible, $1.47\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$, this represents an ideal closed cycle in ${\mathrm{Th}}^{\ensuremath{-}}$ for laser cooling. Furthermore, the zero nuclear spin of $^{232}\mathrm{Th}$ makes the cooling process possible in a Penning trap, which can be used to confine both antiprotons and ${\mathrm{Th}}^{\ensuremath{-}}$ ions. The presented ion dynamics simulations show that the laser-cooled ${\mathrm{Th}}^{\ensuremath{-}}$ anions can effectively cool antiprotons to a temperature around 10 mK.

Gold fluoride is a very unique species. In this work, we reported the resonant photodetachment spectra of cryogenically cooled AuF− via the slow-electron velocity-map imaging method. We determined the electron affinity of AuF to be 17 976(8) cm−1 or 2.2287(10) eV. We observed a dipole-bound state with a binding energy of 24(8) cm−1, a valence excited state with a binding energy of 1222(11) cm−1, and a resonant state with an energy of 814(12) cm−1 above the photodetachment threshold. An unusual vibrational transition with Δn = −3 was observed in the autodetachment from the dipole-bound state. Moreover, two excited states of neutral AuF were recognized for the first time, located at 13 720(78) cm−1 and 16 188(44) cm−1 above the AuF ground state.

This Review presents electron affinities of atoms and structures of atomic negative ions. The negative ion properties of many elements in the main groups of the Periodic Table were well known in the late 20th century. However, our knowledge of the atomic negative ions of transitional elements, lanthanides, and actinides was completely lacking or largely rather qualitative at that time. Substantial progress both on experimental and theoretical sides in this subject has happened during the last two decades. New developments in the experimental methods that yield accurate electron affinities are described in this Review. Based on the previous reviews, a survey of the electron affinity toward the completion of the Periodic Table is presented. A set of atomic electron affinities and energy levels of atomic anions is recommended.

Recent advances in experimental techniques have made it relatively easy to prepare reactant cations in well-defined states of electronic excitation. Extensive studies on the role of excited states in the cation-neutral reactions have contributed significantly to our understanding of reaction kinetics and dynamics. The excited states are often more reactive than the ground state. However, the reactions involving the excited atomic anion are very rare because the negative ions usually have no bound excited states. In the present work, we report the state-specific reaction of Pd anions with H2. Surprisingly, we observed that the ground-state Pd anions react with H2 10 times faster than the excited Pd anions. The high-level calculations show that the difference is due to the reaction barrier.

Electron affinities (EAs) of many lanthanide elements still remain unknown due to their complicated electronic structures and relatively low EA values. In the present work, we utilized the slow-velocity map-imaging method combined with an ion trap to resolve conundrums. The EA values of praseodymium, neodymium, and terbium are determined to be $881.0(37)\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ or 0.109 23(46) eV, $786.3(26)\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ or 0.097 48(31) eV, and $1059.1(64)\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ or 0.131 31(79) eV, respectively. We also observed several excited states of Pr, Nd, and Tb anions.

We report an experimental and theoretical investigation into the dynamics of electron-impact ionization of the unresolved outermost molecular orbitals (6ag + 1b1g) of pyrazine (C4N2H4). Experimental triple differential cross sections (TDCS) are compared with cross sections calculated within a molecular 3-body distorted wave (M3DW) framework. The M3DW theory was able to reproduce the qualitative scattering behaviour in the binary region, but failed to describe the absolute intensity of the TDCS and the recoil scattering behaviour. Momentum profiles were used to identify possible sources where the M3DW may mask the quantum character of the ionized orbitals in describing the ionization dynamics.

Laser cooling is a well-established technique for the creation of ensembles of ultracold neutral atoms or positive ions. This ability has opened many exciting new research fields over the past 40 years. However, no negatively charged ions have been directly laser cooled because a cycling transition is very rare in atomic anions. Efforts of more than a decade currently have La^{-} as the most promising candidate. We report on experimental and theoretical studies supporting Th^{-} as a new promising candidate for laser cooling. The measured and calculated electron affinities of Th are, respectively, 4901.35(48) cm^{-1} and 4832 cm^{-1}, or 0.607 690(60) and 0.599 eV, almost a factor of 2 larger than the previous theoretical value of 0.368 eV. The ground state of Th^{-} is determined to be 6d^{3}7s^{2} ^{4}F_{3/2}^{e} rather than 6d^{2}7s^{2}7p ^{4}G_{5/2}^{o}. The consequence of this is that there are several strong electric dipole transitions between the bound levels arising from configurations 6d^{3}7s^{2} and 6d^{2}7s^{2}7p in Th^{-}. The potential laser-cooling transition is ^{2}S_{1/2}^{o}↔^{4}F_{3/2}^{e} with a wavelength of 2.6 μm. The zero nuclear spin and hence lack of hyperfine structure in Th^{-} reduces the potential complications in laser cooling as encountered in La^{-}, making Th^{-} a new and exciting candidate for laser cooling.

Atomic lanthanum anion ${\mathrm{La}}^{\ensuremath{-}}$ is the best candidate for laser cooling of any atomic anions found so far. The bound-bound electric dipole transitions of ${\mathrm{La}}^{\ensuremath{-}}$ have been identified and measured. Theoretical studies have shown that ${\mathrm{La}}^{\ensuremath{-}}$ has a very complicated electronic structure, which cannot be well resolved by the traditional photoelectron spectroscopy. In the present work, we report high-resolution photoelectron spectroscopy of ${\mathrm{La}}^{\ensuremath{-}}$ via the slow-electron velocity-map imaging method in combination with an ion trap. The electron affinity of La was determined to be $4496.97(20)\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ or 0.557 553(25) eV. In addition, the energy levels of ${\mathrm{La}}^{\ensuremath{-}}$, $^{3}F_{3}^{e}$, $^{3}F_{4}^{e}$, $^{1}D_{2}^{e}$, $^{1}D_{2}^{o}$, $^{3}P_{0}^{e}$, $^{3}P_{1}^{e}$, and $^{3}P_{2}^{e}$, were also determined.

We report a measurement of the valence orbital momentum profiles of tetrabromomethane (${\mathrm{CBr}}_{4}$) using symmetric noncoplanar $(e,2e)$ experiments at the impact energies of about 600 and 1200 eV. The experimental momentum profiles for the individual orbitals $5{t}_{1}, 13{t}_{2}, 5e, 12{t}_{2}$, and $9{a}_{1}$ and the branching ratio of $5{t}_{1}$ to $13{t}_{2}$ and $5e$ to $13{t}_{2}$ are obtained and compared with two kinds of calculations under the plane-wave impulse approximation. One is theoretical momentum profiles that have been calculated at the equilibrium geometry, the other is those that involve vibrational effects using a thermal sampling molecular dynamics method. The calculations considering molecular vibrations are in better agreement with experiment than the equilibrium geometry calculations, indicating the important role of nuclear motions on the valence orbital electronic structures of ${\mathrm{CBr}}_{4}$. The distorted-wave effects are observed in the experimental momentum profiles of $5{t}_{1}, 5e$, and $12{t}_{2}$ which display dynamic dependencies on the impact energies. A multicenter interference or bond oscillation effect has been observed from the momentum profile ratios of $5{t}_{1}$ to $13{t}_{2}$ and $5e$ to $13{t}_{2}$ which has direct information about the bond length of a molecule.

We report an experimental and theoretical investigation of electron-impact single ionization of the highest occupied molecular orbital 1t2 and the next highest occupied molecular orbital 2a1 states of CH4 at an incident electron energy of 250 eV. Triple differential cross sections measured in two different laboratories were compared with results calculated within the molecular 3-body distorted wave and generalized Sturmian function theoretical models. For ionization of the 1t2 state, the binary peak was observed to have a single maximum near the momentum transfer direction that evolved into a double peak for increasing projectile scattering angles, as has been seen for ionization of atomic p-states. A detailed investigation of this evolution was performed. As expected because of its s-type character, for ionization of the 2a1 state, only a single binary peak was observed. Overall, good agreement was found between experiment and theory.

We report a measurement of the valence orbital-momentum profiles of mercury (Hg) using a high-sensitivity binary $(e,2e)$ electron-momentum spectrometer at incident energies of 600 and 1200 eV plus the binding energy. The $6{s}_{1/2}$ orbital and the spin-orbit components of $5{d}_{5/2}$ and $5{d}_{3/2}$ orbitals are well separated in the measured binding-energy spectra. The experimental momentum distributions for the individual orbitals and the branching ratio of $5{d}_{5/2}$ to $5{d}_{3/2}$ are obtained and compared with predictions from a plane-wave impulse approximation (PWIA) in which the orbital wave functions are calculated using the nonrelativistic (NR) and spin-orbital (SO) relativistic theories. The SO relativistic calculations are in better agreement with experiment than the NR, indicating clearly the importance of relativistic effects in the electronic structure of Hg. We also observe some discrepancies between experiment and PWIA calculations in the high-momentum region of $6{s}_{1/2}$ and the low-momentum region of $5d$ orbitals which display a dynamic dependence on the impact energy. These discrepancies become smaller at a higher energy of about 1200 eV and thus can be qualitatively assigned to the distorted-wave effect in the $(e,2e)$ reaction of Hg.

Methane activation by transition metals is of fundamental interest and practical importance, as this process is extensively involved in the natural gas conversion to fuels and value-added chemicals. While single-metal centers have been well recognized as active sites for methane activation, the active center composed of two or more metal atoms is rarely addressed and the detailed reaction mechanism remains unclear. Here, by using state-of-the-art time-of-flight mass spectrometry, cryogenic anion photoelectron imaging spectroscopy, and quantum-chemical calculations, the cooperation of the two Ta atoms in a dinuclear carbide cluster Ta2C4– for methane activation has been identified. The C–H bond activation takes place predominantly around one Ta atom in the initial stage of the reaction and the second Ta atom accepts the delivered H atom from the C–H bond cleavage. The well-resolved vibrational spectra of the cryogenically cooled anions agree well with theoretical simulations, allowing the clear characteriz...

We report both non-resonant and resonant high-resolution photoelectron imaging of cryogenically-cooled deprotonated uracil anions, N1[U-H]−, via vibrational levels of a dipole-bound excited state. Photodetachment spectroscopy of N1[U-H]− was reported previously (Liu et al., 2014), in which forty-six vibrational autodetachment resonances due to the excited dipole-bound state were observed. By tuning the detachment laser to the vibrational levels of the dipole-bound state, we obtained high-resolution resonant photoelectron spectra, which are highly non-Franck–Condon. The resonant photoelectron spectra reveal many Franck–Condon inactive vibrational modes, significantly expanding the capability of photoelectron spectroscopy. A total of twenty one fundamental vibrational frequencies for the N1[U-H] radical are obtained, including all eight low-frequency out-of-plane modes, which are forbidden in non-resonant photoelectron spectroscopy. Furthermore, the breakdown of the Δv = −1 propensity rule is observed for autodetachment from many vibrational levels of the dipole-bound state, due to anharmonic effects. In particular, we have observed intramolecular electron rescattering in a number of resonant photoelectron spectra, leading to excitations of low-frequency vibrational modes. Further theoretical study may be warranted, in light of the extensive experimental data and new observations, to provide further insight into the autodetachment dynamics and vibronic coupling in dipole-bound states, as well as electron molecule interactions.

Atomic clusters are being actively studied for activation of methane, the most stable alkane molecule. While many cluster cations are very reactive with methane, the cluster anions are usually not very reactive, particularly for noble metal free anions. This study reports that the reactivity of molybdenum carbide cluster anions with methane can be much enhanced by adsorption of CO. The Mo2 C2 (-) is inert with CH4 while the CO addition product Mo2 C3 O(-) brings about dehydrogenation of CH4 under thermal collision conditions. The cluster structures and reactions are characterized by mass spectrometry, photoelectron spectroscopy, and quantum chemistry calculations, which demonstrate that the Mo2 C3 O(-) isomer with dissociated CO is reactive but the one with non-dissociated CO is unreactive. The enhancement of cluster reactivity promoted by CO adsorption in this study is compared with those of reported systems of a few carbonyl complexes.

In this work, we study the valence orbital momentum profiles of tetrachloromethane (CCl4) performed with binary (e, 2e) measurements at the impact energies of about 600 and 1200 eV with higher energy-resolution of Δ e ∼ 0.7 eV. The experimental momentum profiles for the molecular orbitals 2 t 1 , 7 t 2 , 2 e , 6 t 2 , and 6 a 1 are obtained and compared with calculations under the plane-wave impulse approximation. The calculations at the equilibrium geometry of CCl4 show generally good agreement with the experimental momentum profiles except for the low momentum range of 2 t 1 and 2 e which is considerable lower than the experiment. The experimental momentum profile shows dynamic dependencies on the impact energies which is ascribed to the distorted-wave effects. Further calculation considering molecular vibrations for the 2 t 1 highest occupied molecular orbital (HOMO) shows a better agreement with experiment than the equilibrium calculation, indicating the important role of nuclear motions on the HOMO electronic structure of CCl4.

Electron affinities (EA) of most lanthanide elements still remain unknown owing to their relatively lower EA values and the fairly complicated electronic structures. In the present work, we report the high-resolution photoelectron spectra of atomic cerium anion Ce− using the slow electron velocity-map imaging method in combination with a cold ion trap. The electron affinity of Ce is determined to be 4840.62(21) cm−1 or 0.600160(26) eV. Moreover, several excited states of Ce− (4H9/2, 4I9/2, 2H9/2, 2G9/2, 2G7/2, 4H13/2, 2F5/2, and 4I13/2) are observed.

Hafnium is the last transition-metal element with an undetermined electron affinity. Using a slow-electron velocity-map imaging spectrometer equipped with a cold ion trap, the electron affinity of hafnium atoms is measured to be $1436(5)\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ or 0.1780(6) eV. The cold ion trap employed in the present measurement is found to be crucial for reducing the background noise from the hafnium hydride anions.

Although early transition metal (ETM) carbides can activate CH bonds in condensed-phase systems, the electronic-level mechanism is unclear. Atomic clusters are ideal model systems for understanding the mechanisms of bond activation. For the first time, CH activation of a simple alkane (ethane) by an ETM carbide cluster anion (MoC3 (-) ) under thermal-collision conditions has been identified by using high-resolution mass spectrometry, photoelectron imaging spectroscopy, and high-level quantum chemical calculations. Dehydrogenation and ethene elimination were observed in the reaction of MoC3 (-) with C2 H6 . The CH activation follows a mechanism of oxidative addition that is much more favorable in the carbon-stabilized low-spin ground electronic state than in the high-spin excited state. The reaction efficiency between the MoC3 (-) anion and C2 H6 is low (0.23±0.05) %. A comparison between the anionic and a highly efficient cationic reaction system (Pt(+) +C2 H6 ) was made. It turned out that the potential-energy surfaces for the entrance channels of the anionic and cationic reaction systems can be very different.

Molecular conformation is important in chemistry and biochemistry. Conformers connected by low energy barriers can only be observed at low temperatures and are difficult to be separated. Here we report a new method to obtain conformation-selective spectroscopic information about dipolar molecular radicals via dipole-bound excited states of the corresponding anions cooled in a cryogenic ion trap. We observed two conformers of cold 3-hydroxyphenoxide anions [m center dot HO(C6H4)O-] in high-resolution photoelectron spectroscopy and measured different electron affinities, 18 850(8) and 18 917(5) cm(-1), for the syn and anti 3-hydroxyphenoxy radicals, respectively. We also observed dipole-bound excited states for m-HO(C6H4)O- with different binding energies for the two conformers due to the different dipole moments of the corresponding 3-hydroxyphenoxy radicals. Excitations to selected vibrational levels of the dipole-bound states result in conformation-selective photoelectron spectra. This method should be applicable to conformation-selective spectroscopic studies of any anions with dipolar neutral cores.

Vibrational state-selective resonant two-photon photoelectron spectra have been obtained via a triplet intermediate state ((3)Σ(-)) of AuS(-) near its detachment threshold using high-resolution photoelectron imaging of cryogenically cooled AuS(-) anions. Four vibrational levels of the (3)Σ(-) excited state are observed to be below the detachment threshold. Resonant two-photon absorptions through these levels yield vibrational state-selective photoelectron spectra to the (2)Σ final state of neutral AuS with broad and drastically different Franck-Condon distributions, reflecting the symmetries of the vibrational wave functions of the (3)Σ(-) intermediate state. The (3)Σ(-) excited state is spin-forbidden from the (1)Σ(+) ground state of AuS(-) and is accessed due to strong relativistic effects. The nature of the (3)Σ(-) excited state is confirmed by angular distributions of the photoelectron images and quantum calculations.

Deprotonated thymine can exist in two different forms, depending on which of its two N sites is deprotonated: N1[T–H]− or N3[T–H]−. Here we report a photodetachment study of the N1[T–H]− isomer cooled in a cryogenic ion trap and the observation of an excited dipole-bound state. Eighteen vibrational levels of the dipole-bound state are observed, and its vibrational ground state is found to be 238 ± 5 cm−1 below the detachment threshold of N1[T–H]−. The electron affinity of the deprotonated thymine radical (N1[T–H]˙) is measured accurately to be 26 322 ± 5 cm−1 (3.2635 ± 0.0006 eV). By tuning the detachment laser to the sixteen vibrational levels of the dipole-bound state that are above the detachment threshold, highly non-Franck–Condon resonant-enhanced photoelectron spectra are obtained due to state- and mode-selective vibrational autodetachment. Much richer vibrational information is obtained for the deprotonated thymine radical from the photodetachment and resonant-enhanced photoelectron spectroscopy. Eleven fundamental vibrational frequencies in the low-frequency regime are obtained for the N1[T–H]˙ radical, including the two lowest-frequency internal rotational modes of the methyl group at 70 ± 8 cm−1 and 92 ± 5 cm−1.

It was believed that the rhenium anion Re– was not stable, just like Mn–. We report the observation of Re– in the laser ablation ion source and the further confirmation via the high-resolution photoelectron spectra of Re–. The ground state of Re– ions is 5d66s2 5D4. The electron affinity of rhenium is determined to be 487.13(51) cm–1 or 60.396(63) meV.

The latest electron affinity value of an iridium atom is 1.564 36(15) eV, determined via a method based on the Wigner threshold law by Bilodeau and co-workers. However, they observed a significant deviation from the Wigner threshold law in the threshold photodetachment experiment. To address this dilemma, we conducted high-resolution photoelectron spectroscopy of Ir− via the slow-electron velocity-map imaging method in combination with an ion trap. The electron affinity of Ir was measured to be 12 614.97(9) cm−1 or 1.564 057(11) eV. We find that the Wigner threshold law is still valid for the threshold photodetachment of Ir− through a p-wave fitting of the photodetachment channel Ir−5d86s23F4→Ir5d86sb4F9/2. The photoelectron angular distributions of photodetachment channels Ir−5d86s23F4→Ir5d76s2a4F9/2 and Ir−5d86s23F4→Ir5d86sb4F9/2 were also investigated. The behavior of anisotropy parameter β indicates a strong interaction between the two channels. Moreover, the energy level 3P2 of Ir−, which was not observed in the previous works, was experimentally determined to be 4163.24(16) cm−1 above the ground state.The latest electron affinity value of an iridium atom is 1.564 36(15) eV, determined via a method based on the Wigner threshold law by Bilodeau and co-workers. However, they observed a significant deviation from the Wigner threshold law in the threshold photodetachment experiment. To address this dilemma, we conducted high-resolution photoelectron spectroscopy of Ir− via the slow-electron velocity-map imaging method in combination with an ion trap. The electron affinity of Ir was measured to be 12 614.97(9) cm−1 or 1.564 057(11) eV. We find that the Wigner threshold law is still valid for the threshold photodetachment of Ir− through a p-wave fitting of the photodetachment channel Ir−5d86s23F4→Ir5d86sb4F9/2. The photoelectron angular distributions of photodetachment channels Ir−5d86s23F4→Ir5d76s2a4F9/2 and Ir−5d86s23F4→Ir5d86sb4F9/2 were also investigated. The behavior of anisotropy parameter β indicates a strong interaction between the two channels. Moreover, the energy level 3P2 of Ir−, which was not obs...

Synopsis In a joint experimental and theoretical collaboration, triple differential cross sections are presented for electron-impact single ionization of the 1t2 and 2a1 states of CH4 at an incident electron energy of 250 eV. Experimental data from two different laboratories are compared with molecular 3-body distorted wave (M3DW) and generalized Sturmian function (GSF) calculations. Overall, we find a good experiment-experiment, and also a relatively good experiment-theories, agreement. We observe that for the 1t2 state, similarly to ionization of atomic p-states, the peak is sometimes doubled.

Synopsis Atomic lanthanum anion La− is the best candidate for laser cooling of any atomic anions by far. The previous theoretical studies showed that La− has very a complicated electronic structure, which cannot be well resolved by the traditional photoelectron spectroscopy. In the present work, we used the slow-electron velocity-map imaging method in combination with an ion trap to measure the electronic structure of La−. The electron affinity of La is accurately determined to be 4496.97(20) cm−1 or 0.557553(25) eV.

We report an experimental and theoretical investigation into the dynamics of electron-impact ionization of R-carvone. Experimental triple differential cross sections are obtained in asymmetric coplanar kinematic conditions for the ionization of the unresolved combination of the three outermost molecular orbitals (41a-39a) of R-carvone. These cross sections are compared with theoretical cross sections calculated within a molecular 3-body distorted wave (M3DW) framework employing either a proper orientation average or orbital average to account for the random orientation of the molecule probed in the experiment. Here, we observe that the overall scattering behavior observed in the experiment is fairly well reproduced within the M3DW framework when implementing the proper average over orientations. The character of the ionized orbitals also provides some qualitative explanation for the observed scattering behavior. This represents substantial progress when trying to describe the scattering dynamics observed for larger molecules under intermediate-impact energy and asymmetric energy sharing scattering conditions.

We exposed single- and double-walled carbon nanotube (SWCNT and DWCNT) fibers to microwave radiation. Small carbon clusters of C2 were detached from the nanotubes, and the process was accompanied by intense heat release. The exfoliation of C2 made the nanotubes break, while the high temperature made the nanotube bundles transform into large diameter CNTs. Strong visible light emission was observed from the vicinity of the nanotube fibers. The emission spectra excited by the microwaves from the as-grown CNT fibers correspond to the Swan band of C2 clusters. In the case of the purified SWCNT fibers, two characteristic peaks at 584 nm and 769 nm emerge in the spectra beyond the Swan band of C2.

Molecules with sufficiently large dipole moments were predicted to form weakly bound negative ions in the dipolar field and such dipole-bound anions have been observed and characterized experimentally. Negative ions with dipolar molecular cores can have excited dipole-bound states (DBSs) near the detachment threshold, analogous to Rydberg states in neutral molecules. DBSs in excited anions were first observed as resonances in photodetachment crosssections. Ultrahigh resolution spectroscopy has been reported on excited DBSs of a number of anions near their detachment threshold by autodetachment. The theory for autoionization from Rydberg states was first developed by Berry, who predicted a Dv= 1 vibrational propensity rule, that is, the Rydberg state undergoes a vibrational relaxation by one vibrational quantum in the molecular core during autoionization, in which the vibrational energy is transferred to the Rydberg electron. The Dv= 1 propensity rule has been observed in autoionization of numerous molecules and mode-specific autoionization has been observed by photoelectron spectroscopy, in which the kinetic energies of the outgoing electrons are measured. The same Dv= 1 propensity rule should apply in autodetachment from DBSs of excited anions and has been inferred in previous studies. However, the electron kinetic energies of the outgoing autodetached electrons from the excited DBSs have not been measured by electron spectroscopy. All prior studies of DBSs in excited anions are dominated by rotational effects and pure vibrational autodetachment from DBSs has not been reported, even though vibrational autodetachment has been observed in weakly bound anions and has been used effectively as a spectroscopic tool for anions. Here we report the direct observation of pure vibrational autodetachment from DBSs of cryogenically cooled phenoxide anions using high-resolution photoelectron imaging. Autodetachment from eight vibrational levels of the DBS in optically exited phenoxide anions are observed and the Dv= 1 propensity rule is found to be strictly obeyed. Three vibrational modes, which have weak Franck–Condon factors in the nonresonant photodetachment, are observed to be dramatically enhanced. Excitation to the bound ground vibrational level of the DBSs of phenoxide is observed using resonant two-photon detachment, allowing the binding energy of the DBSs to be directly measured. The phenoxy radical (C6H5OC) is an important transient specie involved in numerous environmental and biological processes. Its vibrational spectroscopy has been studied in solution and in argon matrices. Photoelectron spectroscopy (PES) of the phenoxide anion (C6H5O ) consists of an extensive vibrational progression in the v11 mode. [30] A recent high-resolution PE imaging study of phenoxide yielded an accurate electron affinity (18178 7 cm ) and a v11 vibrational frequency (519 cm ) for the phenoxy radical. The current experiments are carried out using a PES apparatus equippedwith an electrospray ionization source, a cryogenically controlled ion trap, and a high-resolution PE imaging system. The phenoxide anions were produced by electrospray of a mixed phenol/sodium hydroxide solution. Anions from the electrospray source were transported into a temperature-controlled ion trap, where they were accumulated and cooled for 0.1 s before being ejected into the extraction zone of a time-of-flight mass spectrometer. A dye laser was used in the current study and the imaging system was calibrated using the known spectra of Au . The resolution of the imaging system has been described recently and can reach about 2 cm 1 for low-energy electrons. The PE images and spectra at 20 K are shown in Figure 1 at four photon energies. These data are similar to those reported recently, with two important differences. First, the cryogenically cooled ions completely eliminate the vibrational hot bands and result in narrower line widths. The 0 !0 transition (00 ) in Figure 1a reveals rotational contours (see inset) and defines a more accurate electron affinity of 18173 3 cm 1 for the phenoxy radical. More importantly, in addition to the dominating v11 vibrational progression, vibrational transitions with weak Franck–Condon factors are observed, that is, modes v9, v10, and v18 and their combination bands with mode v11. The modes v9 and v10 are both totally symmetric with a1 symmetry, [29,35] similar to mode v11, and are allowed transitions. However, mode v18 has b1 symmetry and its activity must be due to vibronic couplings, as observed recently in high-resolution PE imaging of other small polyatomic anions. The angular distributions of all the vibrational peaks because of the a1 modes display splus dorbital characters, consistent with the p-type orbital from which the electron is detached. The angular distributions of the vibrational peaks because of the v18 mode are different, displaying distinct p-orbital character (Figure 1). The different angular distributions for the different vibrational modes are interesting and can be used in vibrational assignments in [*] Dr. H. T. Liu, D. L. Huang, P. D. Dau, Prof. Dr. L. S. Wang Department of Chemistry, Brown University Providence, RI 02912 (USA) E-mail: Lai-Sheng_Wang@brown.edu

We report the high-resolution photoelectron spectra of negative vanadium ions obtained via the slow-electron velocity-map imaging method. The electron affinity of V was determined to be 4255.9(18) cm

Single crystal reflects the intrinsic physical properties of a material, and single crystals with high-crystalline quality are highly desired for the acquisition of high-performance devices. We found that large single crystals of perovskite CH3NH3PbI3(Cl) could be grown rapidly from chlorine-containing solutions. Within 5 days, CH3NH3PbI3(Cl) single crystal as large as 20 mm × 18 mm × 6 mm was harvested. As a most important index to evaluate the crystalline quality, the full width at half-maximum (fwhm) in the high-resolution X-ray rocking curve (HR-XRC) of as-grown CH3NH3PbI3(Cl) single crystal was measured as 20 arcsec, which is far superior to so far reported CH3NH3PbI3 single crystals (∼1338 arcsec). The unparalleled crystalline quality delivered a low trap-state density of down to 7.6 × 10(8) cm(-3), high carrier mobility of 167 ± 35 cm(2) V(-1) s(-1), and long transient photovoltaic carrier lifetime of 449 ± 76 μs. The improvement in the crystalline quality, together with the rapid growth rate and excellent carrier transport property, provides state-of-the-art single crystalline hybrid perovskite materials for high-performance optoelectronic devices.

Experimental and theoretical triple differential cross sections for intermediate-energy (250 eV) electron-impact single ionization of the ${\mathrm{CO}}_{2}$ are presented for three fixed projectile scattering angles. Results are presented for ionization of the outermost $1{\ensuremath{\pi}}_{g}$ molecular orbital of $\mathrm{C}{\mathrm{O}}_{2}$ in a coplanar asymmetric geometry. The experimental data are compared to predictions from the three-center Coulomb continuum approximation for triatomic targets, and the molecular three-body distorted wave (M3DW) model. It is observed that while both theories are in reasonable qualitative agreement with experiment, the M3DW is in the best overall agreement with experiment.