3Φ States Research Articles

Ultrafast Transient Absorption Spectroscopy of UO22+ and [UO2Cl]+

For the only water coordinated "free" uranyl(VI) aquo ion in perchlorate solution we identified and assigned several different excited states and showed that the 3Δ state is the luminescent triplet state from transient absorption spectroscopy. With additional data from other spectroscopic methods (TRLFS, UV/vis) we generated a detailed Jabłoński diagram and determined rate constants for several state transitions, like the inner conversion rate constant from the 3Φ state to the 3Δ state transition to be 0.35 ps-1. In contrast to luminescence measurements, it was possible to observe the highly quenched uranyl(VI) ion in highly concentrated chloride solution by TAS and we were able to propose a dynamic quenching mechanism, where chloride complexation is followed by the charge transfer from the excited state uranyl(VI) to chloride. This proposed quenching route is supported by TD-DFT calculations.

Optical Zeeman Spectroscopy of the (0, 0) Bands of theB3Π–X3Δ andA3Φ–X3Δ Transitions of Titanium Monoxide, TiO

The Zeeman effect on lines in the (0, 0) band of the B 3Π-X 3Δ (γ') system and in the (0, 0) band of the A 3Φ-X 3Δ (γ) system of titanium monoxide, TiO, have been recorded and analyzed. Magnetic tuning of the low rotational spectral features recorded at high resolution (FWHM 35 MHz) and at field strengths of up to 1.2 kG is accurately modeled using an effective Zeeman Hamiltonian. A comparison is made with previous predictions, which were based on field-free spectroscopic parameters. It is shown that the large Λ-doubling in the B 3Π state necessitates the inclusion of ΔJ = ±1 matrix elements in the representation of the effective Hamiltonian operator. The observed spectra could only be modeled by allowing the electronic spin and orbital magnetic g-factors, gS and gL, of the B 3Π and A 3Φ states to deviate from 2.002 and 1.000. Nonadiabatic mixing with the nearby C 3Δ state is proposed as the cause of these deviations.

Rotational and hyperfine analysis of the near infrared Φ43–X 3Φ4 transitions of CoCl and CoI

Electronic transitions of cobalt monochloride and cobalt monoiodide have been studied using laser vaporization–reaction free jet expansion and laser induced fluorescence spectroscopy in the near infrared region. The observed transitions have been identified as the [10.3] Φ43–X 3Φ4 transition of CoCl and [11.0] Φ43–X 3Φ4 transition of CoI. The magnetic hyperfine structure arising from the cobalt nucleus with I=7/2 was resolved and analyzed. Accurate rotational and hyperfine parameters for the [10.3] Φ43 and X 3Φ4 states of CoCl and [11.0] Φ43 and X 3Φ4 states of CoI have been obtained. Comparison of Fermi contact parameters, bF, for the upper states indicated that the observed [10.3] Φ43–X 3Φ4 transition of CoCl and [11.0] Φ43–X 3Φ4 transition of CoI have arisen from the promotion of an electron from the bonding σ orbital to a slightly antibonding σ orbital. Observed low-lying Φ3 states of the cobalt monohalides and hydride are also compared and discussed.

Visible laser spectroscopy of cobalt monofluoride

The laser-induced fluorescence excitation spectrum of jet-cooled CoF molecules has been studied in the range of 18 800–22 000 cm −1. Ten observed vibronic bands have been classified into three transitions with the 0–0 band at 18 909, 19 236, and 20 654 cm −1, assigned as the [18.8] 3Φ 4– X 3Φ 4, [19.2] 3Φ 4– X 3Φ 4, and [20.6] 3Γ 5– X 3Φ 4 transition, respectively, the two 3Φ states, [18.8] 3Φ and [19.2] 3Φ, are consistent with Adam’s results (10). The previously unanalyzed [20.6] state is identified in the current work. A rotational analysis of [20.6] 3Γ 5– X 3Φ 4 transition has been performed and effective equilibrium molecular constants have been determined for the first time. In addition, lifetime measurements of the three electronic transitions were carried out under the collision-free condition. From the lifetime analysis, we consider that the V=1, 2, and 3 vibrational levels of [18.8] 3Φ state are perturbed by another state.

The [20.4] 3Φ→(1) 3Δ Green System of LaF

Electronic bands belonging to the [20.4] 3Φ→(1) 3Δ system have been observed in the emission spectrum of lanthanum monofluoride at high temperature in the presence of the Ar + 457.9-nm laser line: the (0–0), (1–1), (2–2), and (3–3) bands of the 3Φ 4→ 3Δ 3 subsystem and the (0–0) bands of the 3Φ 3→ 3Δ 2 and 3Φ 2→ 3Δ 1 subsystems. Rotational structures which are well developed in these experimental conditions were analyzed. The data were treated using a polynomial expression for the upper levels term-values, directly at equilibrium for 3Φ 4, whereas a previous Hamiltonian matrix representation of the (1) 3Δ state was assumed. A Hund's case (a) representation of the [20.4] 3Φ state at v=0 was also considered. Perturbations affecting 3Φ 2 levels at v=0 were observed; the energy and rotational constant of the perturbing state and the interaction parameter were estimated.

A Hund's Case (a) Analysis of the [18.8]3Φi–X3Φi Electronic Transition of CoF

We have recently observed a weak electronic subband near 513 nm in the electronic spectrum of cobalt monofluoride. A rotational analysis has led to its identification as a 3Φ3–X3Φ4 subband where ΔΣ=−1 and ΔΩ=−1. This critical datum has been used in combination with our previously published data (A. G. Adam et al., 1994, Chem. Phys. Lett.230, 82) to obtain a Hund's case (a) analysis for the [18.8]3Φi–X3Φi transition of CoF. The spectroscopic constants and electronic states of CoF are compared to those of CoH and Co+. Two distinct excited 3Φ electronic state vibrational progressions have also been identified in the CoF spectra. The band positions and rotational constants have been used to calculate equilibrium constants for the excited 3Φ states. The two electronic transitions are identified as the K3Φi–X3Φi and L3Φi–X3Φi transitions based on comparisons with CoH.

Ground-State Reversal by Matrix Interaction: Electronic States and Vibrational Frequencies of CUO in Solid Argon and Neon

A 3Φ state is found for the CUO molecule (made by reaction of laser-ablated U and CO) trapped in solid argon, in contrast to the 1Σ+ ground state in solid neon. The new electronic state results from the transfer of an electron from a U−C bonding orbital to a nonbonding 5f orbital of the U atom, thus decreasing the U−C stretching frequency significantly. Infrared spectroscopy and relativistic DFT calculations have been used to characterize these two low-lying states of CUO.

Study of the low-lying states of NiO− and NIO using anion photoelectron spectroscopy

The 2.33 and 3.49 eV photoelectron spectra of NiO− obtained with a new apparatus using field-free electron energy analysis are reported. The electron affinity of NiO is determined to be 1.470(3) eV. A spin–orbit splitting of 260(40) cm−1 for the ground Π2 anion state is observed. A bond length of 1.668(4) Å and vibrational frequency of 660(40) cm−1 are determined from spectral simulations of the neutral Σ-3 ground state←anion Π3/22 state transition. A transition from an excited Σ-4 anion state [Te=900(40) cm−1, ω=760(40) cm−1] to the ground neutral state is assigned. New spectroscopic constants are obtained for the Φ3 state [Te=0.65(1) eV], the Δ1 state [Te=0.94(1) eV, ω=615(15) cm−1, and re=1.600(6) Å] and the second Π3 state [Te=1.194(10) eV, 2A=411(30) cm−1]. These findings are in general agreement with those recently reported by Wu and Wang [J. Chem. Phys. 107, 16 (1997)], although several reassignments of the photoelectron spectra (PES) are made based on comparison with calculations and newly resolved fine structure.

Rotational and Hyperfine Analysis of the A′3Φ4-X3Φ4 Transitions of CoH and CoD

Three new bands of CoH and five new bands of CoD have been observed using laser excitation in the visible and near-infrared, following reaction of Co atoms with H2 or D2 under supersonic jet-cooled conditions. All the bands reported here, together with two reported previously by Varberg et al. (J. Mol. Spectrosc.138, 630-637, 1989), are shown to belong to a single electronic transition with an origin near 12 400 cm−1, here designated A′3Φ4-X3Φ4. High-resolution spectra of the (0, 0) bands of both CoH and CoD reveal extensive hyperfine structure associated with the 59Co nucleus, which shows that the electron configuration of the A′3Φ state is (7σ)1 (3dδ)3(3dπ)3(8 σ)1. Wavelength-resolved fluorescence from one of the CoD bands has given the Ω = 4-3 spin-orbit interval for the X3Φ state as 729 cm−1 and confirmed the presence of a low-lying Ω = 3 electronic state ∼ 2444 cm−1 above the ground state.

Rotational Spectroscopy of the CoH Radical in Its Ground 3Φ State by Far-Infrared Laser Magnetic Resonance: Determination of Molecular Parameters

Five rotational transitions of CoH in its ground 3Φ state have been detected by far-infrared laser magnetic resonance, three in the lowest Ω = 4 component and two in the Ω = 3 component. All the Zeeman transitions show an octet hyperfine pattern due to the 59Co nucleus ( I = 7/2). The much smaller proton doubling was also resolved for most transitions. The data have been fitted to experimental accuracy by an effective Hamiltonian for a molecule in an isolated 3Φ state. The electron orbital and spin g factors determined by the data confirm conclusively that the ground state of CoH is a 3Φ state. The accurate measurement of the rotational constant allows the equilibrium bond length to be determined: r e = 0.15138435(80) nm. A small Λ-type doubling was resolved in the 3Φ 3 component, suggesting the proximity of a 3Σ state among the low-lying electronic states. The cobalt hyperfine splittings have been fitted to determine magnetic dipole and electric quadrupole parameters, which are interpreted in terms of the dominant configuration description for the 3Φ ground state.

Laser spectroscopy of the low-lying electronic states of NbN: Electron spin and hyperfine effects in the states from the configurations σδ and δπ

Rotational and hyperfine analyses have been carried out for the (0,0) bands of the C 3Π–X 3Δ, e 1Π–X 3Δ, and f 1Φ–a 1Δ transitions of gaseous NbN from laser excitation spectra taken at sub-Doppler resolution. The δπ C 3Π and e 1Π states lie only 102 cm−1 apart in zero order but the spin–orbit matrix element between them, which is the sum of the spin–orbit constants for the δ and π electrons, is 698 cm−1; as a result the 3Π1 spin component lies below both the 3Π0 and 3Π2 components, and its hyperfine structure is highly irregular. This irregularity is an extreme example of how cross terms between the spin–orbit interaction and the Fermi contact hyperfine operator alter the apparent value of the hyperfine a constant, the coefficient of I⋅L in the magnetic hyperfine Hamiltonian. Molecular parameters for the C 3Π and e 1Π states have been obtained from a combined fit to the two of them. Including data for the B 3Φ state recorded earlier [Azuma et al., J. Chem. Phys. 91, 1 (1989)], detailed information is now available for all six of the electronic states from the electron configurations σδ and δπ. It has been verified that the spin–orbit/Fermi contact cross terms cause roughly equal and opposite shifts in the hyperfine a constants for the singlet states and the Σ=0 components of the triplet states. After allowing for this effect, it has been possible to interpret the hyperfine a constants in terms of one-electron parameters for the δ and π electrons, in similar fashion to spin–orbit parameters. Wavelength resolved fluorescence, following selective laser excitation of the C 3Π, e 1Π, and f 1Φ states, has led to the discovery of three new electronic states, δ2 c 1Γ, δ2 A 3Σ−, and σ2 b 1Σ+, besides giving the absolute position of a 1Δ. Strong configuration interaction mixing is found to occur between the σ2 b 1Σ+ and δ2 d 1Σ+ states. The low-lying electronic states of NbN are now well understood.

Spin–orbit distortion of the hyperfine structure in heavier molecules: Breakdown of the case (aβ) formalism in the B 3Φ–X 3Δ system of gaseous NbN

A detailed analysis of the rotational and hyperfine structure of the (0,0) band of the B 3Φ–X 3Δ electronic transition of NbN has been performed from sub-Doppler spectra taken with linewidths of about 50 MHz. The Nb hyperfine structure is impressively wide in both states, but particularly so in X 3Δ where one of the unpaired electrons occupies a σ orbital derived from the metal 5s orbital. The electron spin and hyperfine structures do not follow the expected case (aβ ) coupling because of extensive second order spin-orbit effects. It is shown that the asymmetry in the spin–orbit structure of X 3Δ is explained almost quantitatively by interaction with a 1 Δ state from the same electron configuration (which lies at 5197 cm−1); also cross terms between the spin–orbit and Fermi contact interactions in the matrix element 〈3Δ2‖H‖1Δ〉 produce a large correction to the apparent coefficient of the I⋅L magnetic hyperfine interaction in X 3Δ2. The hyperfine structure in a triplet state turns out to be extremely sensitive to the details of the electron spin coupling, and reversals in the sense of the hyperfine structure in the 3Φ4–3Δ3 and 3Φ2–3Δ1 subbands are shown to be consistent with the3Δ state being a regular spin–orbit multiplet (A>0). Particular care has been taken with the calibration, which has meant that extra terms have needed to be added to the magnetic hyperfine Hamiltonian to account for the spin–orbit distortions: instead of the usual three parameters needed in case (aβ ) coupling, the B 3Φ state has required four parameters and the X 3Δ state has required five. The model explains the data very well, and the standard deviation in the least-squares fit to more than 1000 hyperfine line frequencies was 0.000 58 cm−1 (17 MHz).

Electronic structure of FeO and RuO

The electronic structure of FeO and RuO is examined using multiconfiguration self-consistent-field (MC-SCF) wave functions that go asymptotically to minimally correlated fragment atoms. Core electrons are eliminated by the use of relativistic effective potentials (REP) which also are used to calculate the spin-orbit coupling constant for the 5Δ, 5Π, and 5Φ states. The electronic structure of the FeO and RuO 5Δ states is described in terms of interacting singly charged ions, M+ and O−, which are bound primarily by a strong sigma bond. The natural orbitals are determined and evaluated in detail. The characteristics of these orbitals are used to hypothesize an aufbau for the ground states of most of the first and second row transition metal oxides. In addition to the 5Δ states, the 5Σ+, 5Π, 5Φ, 5Σ−, 5Γ, 7Σ+, 7Π, 7Φ, 3Δ, 3Σ+, 3Π, and 3Φ states were also studied. FeH and RuH 6Δ, 4Δ, and 4Φ states were also examined to evaluate the basis set.

Laser photoluminescence of zirconium oxide at 4 K

Laser induced photoluminsecence spectra of ZrO trapped in Ne at 4 K have been obtained. Continuous wave tunable dye and cw argon ion lasers were used to excite ZrO from the X 1Σ+ ground state to the e 1Π and B 3Π electronic states, respectively. Red emission from e 1Π (v=0) →X 1Σ+(v=0,1,2) was observed. In addition, e 1Π (v=0) and e 1Π (v=2) have been found to undergo matrix induced intersystem relaxation into the E 3Π and A 3Φ states, respectively. Infrared emissions of ZrO have been observed and tentatively identified as belonging to E 3Π→X′ 3Δ and e 1Π→c 1Δ. Bandheads of observed transitions are shifted not more than 2% from known gas-phase values. Line shapes of the transitions to the ground state from the e and B states are characterized by a sharp zero-phonon line accompanied by a multiphonon sideband. An additional system overlapping the e 1Π−X 1Σ+ system has been observed and is identified as the A 3Φ2→X′ 3Δ1 band system. The energy of the low-lying c1Δ and X′ 3Δ states are determined to be 5200 and 1650 cm−1 above the ground state.

SCF Method for Excited States. The A3Φ State of BN

SCF Method for Excited States. The <i>A</i>3Φ State of BN