Doppler-free two-photon absorption spectroscopy of trans-glyoxal under magnetic fields up to 6T

In order to measure the Doppler-free two-photon absorption (DFTPA) spectrum in the presence of a strong magnetic field, a sample cell placed in an optical resonator was installed at the centre of the bore of a superconducting magnet capable of generating a magnetic field of up to 6T. Changes in spectra of the A ¹A_u ← X ¹A_g transition of trans-glyoxal were measured as a function of magnetic field strength. Level crossings induced by Zeeman energy shifts were observed. The perturbing level, which shows hyperfine splitting, was identified as the ³A_u(nπ?) state, because the hyperfine splitting is small in the ³B_u(^ππ?) state and large in the ³A_u(nπ?) state. The perturbation between the A ¹A_u(nπ?) and ³A_u(nπ?) states was shown to take place by either vibronic interaction or Zeeman interaction between the ³A_u(nπ?) state and the ³B_u(ππ?) component mixed to the A ¹A_u(nπ?) state by spin-orbit interaction. The magnetic moment of the A ¹A_u state was determined to be approximately 0.0028μ_B, and the magnitude of the mixing coefficients 〈1 ³B_u|H _so|1 ¹A_u〉/[E(1 ¹A_u) ? E(1 ³B_u)] was evaluated to be 0.026.     

Singlet-triplet anticrossings between ungerade states of H2

Singlet-triplet anticrossings in the H₂ molecule have been observed between two ungerade states, B′(3p)¹Σ_u⁺ and f(4p)³Σ_u⁺. This is the first time that an observed H₂ anticrossing has involved a state which can radiate directly to the ground state. Analysis yields accurate values for the zero field separations between two pairs of rotational and vibrational levels. It also yields a value for the Fermi contact interaction in the triplet state as well as the difference in the orbital angular momentum g factors for the two states. From linewidth measurements, we deduce a rigorous lower limit to the radiative lifetime of the B′¹Σ_u⁺ state and a (nearly equal) most reasonable value for it. It is shown that the perturbation between the two states is quite weak leading to little singlet-triplet mixing in zero field. The experimental data establish that the oscillator strength for the forbidden transition from the ground state to the f(4p)³Σ_u⁺ state is at least seven orders of magnitude smaller than that of the allowed transition to the B′¹Σ_u⁺ state.     

Extensive spectroscopic calculations on 12 low-lying electronic states of AlN molecule including transition properties

Using the CASSCF method followed by the internally contracted MRCI approach in combination with the correlation-consistent basis sets, the potential energy curves (PECs) are calculated for the X³Π, A³Σ^-, B³Σ⁺, C³Π, E³Δ, a¹Σ⁺, b¹Π, c¹Δ, d¹Σ⁺, e¹Π, 2³Σ^? and 3³Σ^? electronic states of AlN molecule for internuclear separations from 0.1 to 1.0 nm. All the electronic states correlate to the three dissociation channels, Al(²P_u) + N(⁴S_u), Al(²P_u) + N(²D_u) and Al(²P_u) + N(²P_u). Of these 12 electronic states, only the 2³Σ^? possesses the double well. The PECs determined by the internally contracted MRCI approach are corrected for size-extensivity errors by means of the Davidson correction. The convergent behavior of present calculations is observed with respect to the basis set and level of theory. The effect of core-valence correlation and scalar relativistic corrections on the spectroscopic parameters is discussed. Scalar relativistic correction calculations are performed by the third-order Douglas-Kroll Hamiltonian approximation at the level of cc-pVTZ basis set. Core-valence correlation corrections are included with a cc-pCVTZ basis set. All the PECs are extrapolated to the complete basis set limit. The spectroscopic parameters are evaluated by fitting the first ten vibrational levels when available, which are obtained by solving the ro-vibrational Schrödinger equation with the Numerov’s method. The spectroscopic parameters are compared with those reported in the literature. Excellent agreement is found between the present results and the measurements. Analyses show that the spectroscopic parameters reported in this paper can be expected to be reliably predicted ones. The Franck-Condon factors and radiative lifetimes of the transitions from the A³Σ^?, B³Σ⁺, C³Π, a¹Σ⁺ and b¹Π electronic states to the ground state are calculated for several low vibrational levels, and some necessary discussion has been made.     

Ab initio calculation of transition dipole moments for transitions between valence states in oxygen molecules

Results of ab initio calculations of potential-energy curves for 20 singlet and 20 triplet valence states of oxygen with configuration interaction taken into account in the 6-31G basis are presented. Transition dipole moments of triplet-triplet (1³Π_g ← B ³Σ _u ^? , 1³Π_g ← A ³Σ _u ⁺ , 1³Π_g ← A′ ³Δ_u, B ³Σ _u ^? ← X ³Σ _g ^? , 2³Π_u ← 1³Π _g, 2³Σ _g ^? ← B ³Σ _u ^? , 1³Π_u ← X ³Σ _g ^? , 2³Π_u ← X ³Σ _g ^? , 2³Π _g ← A′³Δ_u, 3³Π_g ← A′ ³Δ _u, 2³Δ_u ← 2³Π_g, 3³Π_g ← B ³Σ _u ^? , and 2³Π_g ← A ³Σ _u ⁺ ) and singlet-singlet (2¹Σ _g ⁺ ← 2¹Π_u, 2¹Π_u ← 1¹Π ^g, ¹Π_u ← 2¹Δ_g, 1¹Π_g ← c ¹Σ _u ^? , ¹Π_u ← b ¹Σ _g ⁺ , 1¹Δ _u ← a ¹Δ_g, 2¹Π_u ← a ¹Δ_g, 2¹Δ_g ← 1¹Δ_u, ¹Π _u ← a ¹Δ _g, 1¹Π_u ← b ¹Σ _g ⁺ , 2¹Π_g ← 1¹Π_u, 2¹Π _g ← c ¹Σ _u ^? , 1¹Δ _u ← 1¹Π _g, f′Σ _u ⁺ ← b ¹Σ _g ⁺ , 2¹Σ _g ⁺ ← f ′¹Σ _u ⁺ , 3¹Π_g ← 1¹Δ_u) radiative transitions are calculated as functions of internuclear separation. The possibility of observing these transitions under experimental conditions is discussed.     

Accurate spectroscopic calculations of the 19 Λ-S states and 36 Ω states of the BC+ cation

This work computed the potential energy curves of 19 Λ-S states, which arose from the first five dissociation limits of BC⁺ cation, B⁺(¹S_g) + C(³P_g), B⁺(¹S_g) + C(¹D_g), B⁺(¹S_g) + C(¹S_g), C⁺(²P_u) + B(²P_u), and B⁺(¹S_g) + C(⁵S_u). The calculations were done for internuclear separations from 0.08 to 1.07 nm. The potential energy curves of 36 Ω states yielded from these Λ-S states were also calculated. Core-valence correlation and scalar relativistic correction, basis set extrapolation as well as Davidson correction were accounted for. Of these Λ-S states, the c¹Σ⁺, D³Π, 2¹Π, 2³Σ⁺, 2¹Δ, 3¹Σ⁺, and 4¹Σ⁺ had double wells; the 3³Π and 3¹Π states had three wells; the C³Σ^? and D³Π states were inverted with the spin-orbit coupling effect included; and the second wells of c¹Σ⁺, D³Π and 3¹Σ⁺ states, the second and the third wells of 3³Π state as well as the third well of 3¹Π state were very weakly bound, which well depths were smaller than 400 cm^?1. The spectroscopic parameters were determined for all the states. The vibrational properties were predicted only for some weakly bound states. The spin-orbit coupling effect on the spectroscopic parameters was evaluated.     

Accurate theoretical spectroscopic investigations of the 20 Λ-S and 58 Ω states of O2+ cation including the spin–orbit coupling effect

The potential energy curves (PECs) are calculated for the 20 Λ-S states (X²Π_g, A²Π_u, B²Σ^?_g, a⁴Π_u, b⁴Σ^?_g, b′⁴Π_g, c⁴Σ^?_u, 1²Σ⁺_g, 1²Σ⁺_u, 1²Σ^?_u, 1⁴Σ⁺_g, 1⁴Σ⁺_u, 1⁴Δ_g, 1⁴Δ_u, 1⁶Σ⁺_g, 1⁶Σ⁺_u, 1⁶Π_g, 1⁶Π_u, 2⁴Π_g and 2⁴Π_u) of O₂⁺ cation and their corresponding 58 Ω states. Of these 20 Λ-S states, the 1⁶Π_u state is found to be repulsive. The 1²Σ⁺_g, 1⁴Σ⁺_u, c⁴Σ^?_u and 1⁴Δ_u states are found to possess the double well. The b⁴Σ^?_g, 1⁶Σ⁺_g, 1⁴Σ⁺_u, a⁴Π_u, A²Π_u, 1⁶Π_g and 2⁴Π_g states are found to be inverted with the spin–orbit coupling effect included. The b′⁴Π_g, 1⁶Π_g, 1⁶Σ⁺_g, 1⁴Σ⁺_u and 1⁴Δ_u states, and the second well of the 1²Σ⁺_g state are found to be the weakly bound states. The b′⁴Π_g state is found to possess one well with one barrier. The PECs are calculated by the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson correction in combination with the aug-cc-pV6Z basis set. The core–valence correlation and scalar relativistic corrections are included. The convergent behaviour of present calculations is discussed with respect to the basis set and theoretical level. The spin–orbit coupling effect is accounted for. The PECs are extrapolated to the complete basis set limit. The spectroscopic parameters are evaluated, and compared with available measurements. It demonstrates that the spectroscopic parameters reported here can be expected to be reliably predicted ones.     

NMR 1 J(HD) coupling in HD as a function of interatomic distance in the presence of an external magnetic field

A theoretical study has been made of the dependence of the ¹ J(HD) coupling in HD on the interatomic distance R in the presence of a static uniform magnetic field B ₀. The behaviour of all coupling terms arising from Ramsey's magnetic electron-nucleus interactions, Fermicontact (FC), spin-dipolar (SD) and paramagnetic (PSO) and diamagnetic (DSO) spin-orbital interactions is analysed qualitatively for large R. It is concluded that the PSO, DSO and SD terms become negligibly small as R increases. Detailed calculations were carried out for the FC term following two different approaches: detailed full CI calculations within a non-perturbative approach; and explicit diagonalization of the Hamiltonian operator restricted to the subspace spanned by the ¹Σ⁺;_g and the ³Σ⁺;_u states. Within the approximations considered, the FC term of ¹ J(HD) is found to be independent of B ₀ and to increase by several orders of magnitude, in agreement with previous results by Bacskay, G. B., 1995, Chem. Phys. Lett., 242, 507, until a critical distance R(B ₀) is reached, beyond which it almost vanishes. The quenching of the coupling at R(B ₀) is due to the splitting of the ³Σ⁺;_u state in the presence of the field B ₀. The stronger the field the shorter is R(B ₀).     

Interaction of Zn atoms in the 1 S and 3 P states with N2 molecules in the X 1Σ g + and A 3Σ u + states at moderate distances between the atom and molecule

An asymptotic method was used to derive analytical expressions for the matrix elements of interaction between the N₂ molecule in the X ¹Σ _g ⁺ and A ³Σ _u ⁺ electronic states and the Zn atom in the ¹ S and ³ P states. Quadrupole-quadrupole, dispersion, and exchange interactions were taken into consideration. The character of the set of diabatic vibronic potential energy surfaces of the system suggests that the energy transfer in the process N₂(A ³Σ _u ⁺ ) + Zn(¹ S) → N₂(X ¹Σ _g ⁺ ) + Zn(³ P) may prove to be rather effective.     

Diagnosis of OH radical by optical emission spectroscopy in a wire-plate bi-directional pulsed corona discharge

The emission spectrum of the molecule OH (A²Σ→X²Π, 0–0) during a high-voltage, bi-directional pulsed corona discharge consisting of a gas mixture of N₂ and H₂O in a wire-plate reactor has been successfully recorded under severe electromagnetic interference at atmospheric pressure. The relative vibrational populations and the vibrational temperature of N₂ (C, v′) have also been determined. Due to the difficulty of determining the exact overlapping spectral line shape function of the OH (A²Σ→X²Π, 0–0) and the Δv=+1 vibrational transition band of N₂ (C³Π_u→B³Π_g), a practicable Gaussian form is used for calculating the emission intensity of OH (A²Σ→X²Π, 0-0) and the Δv=+1 vibrational transition band of N₂ (C³Π_u→B³Π_g). The emission intensity of OH (A²Σ→X²Π, 0–0) has been evaluated with a satisfactory accuracy by subtracting the emission intensity of the Δv=+1 vibrational transition band of N₂ (C³Π_u→B³Π_g) from the overlapping spectra. The relative population of OH (A²Σ) has been obtained by the emission intensity of OH (A²Σ→X²Π, 0–0) and Einstein's transition probability. The influences of peak voltage, pulse repetition rate and O₂ flow rate on the relative population of OH (A²Σ) radicals have also been investigated. We found that the relative population of OH (A²Σ) rises with an increase in both the peak applied voltage and the pulse repetition rate. When oxygen is added to an N₂ and H₂O gas mixture, the relative population of OH (A²Σ) radicals decreases exponentially with an increase in added oxygen. The main physicochemical processes involved are also discussed in this paper.     

Effect of magnetic field on luminescence of MgS,CaS and CaO phosphors activated with Bi3+ ions

The magnetic field dependence of the intensity I(A₀) of the zero-phonon line of the ³A_1u → ¹A_1g emission band is measured at 4.2 K for MgS, CaS and CaO phosphors activated with Bi³⁺ ions. The increase in I(A₀) is proportional to the square of the external magnetic field. The results are compared with those for Pb²⁺-activated phosphors.     

Quenching of SO2 phosphorescence by a magnetic field

Phosphorescence excitation spectra of the ã³B₁← [Xtilde]¹A₁ transition of SO₂ were measured in the absence and presence of a magnetic field (B = 0?44 T², P(SO₂) = 0?7 Torr). The absorption and phosphorescence excitation spectra of the ã³B₁← [Xtilde]¹A₁ transition of SO₂ measured in the absence of a magnetic field show that the relative intensity of the bands of the phosphorescence excitation spectrum is smaller than the relative intensity of the corresponding bands of the absorption spectrum beginning with the (0, 2, 0) band. In the presence of a magnetic field, the intensity of the phosphorescence excitation band falls, for ν_exc> 26400 cm^-1. Under the direct excitation of the ã³B₁← [Xtilde]¹A₁ transition, the dependence of the magnetic quenching of the SO₂ phosphorescence on the excitation frequency (ν_exc) was studied at P(SO₂) = 0?7 Torr and B = 0?44 T. The dependence of the magnetic field effect on ν_excshows that only the vibrationally excited levels of the ã³B₁ state are sensitive to an external magnetic field. The magnetic field strength and the pressure dependence of the magnetic field effects were studied under indirect excitation of the ã³B₁← [Xtilde]¹A₁ transition at λ_exc = 308 nm. The magnetic field and the pressure dependence were investigated for pure SO₂ and for SO₂ + RH (RH n-C₅H₁₂) mixtures. It was found that the magnetic field effect was saturated at B ? 0?25 T. The saturation value (Gr = l(0?3 T)/l(0)) increases with increasing gas pressure. The magnetic field, the pressure and the excess vibrational energy (ν_excess) dependence of the magnetic quenching of SO2 phosphorescence show that the data observed can be explained by an indirect mechanism within the framework of a low level density approximation.     

Electron-vibrational energy exchange in collisions of electronically excited N2(A 3Σ u + ) molecules with Zn(X 1 S) atoms

The interaction matrix between the N₂ molecule in the X ¹Σ _g ⁺ and A ³Σ _u ⁺ states and the Zn atom in the ¹ S and ³ P states calculated earlier by the asymptotic method was used to find the rate constants for the electron-vibrational energy exchange N₂(A ³Σ _u ⁺ , v) + Zn(¹ S) → N₂(X ¹Σ ₈ ⁺ , v′) + Zn(³ P). The calculations were performed by the transition state method, and the probabilities of transitions between intersecting electron-vibrational terms of the system in motion along the reaction coordinate were determined by the Landau-Zener equation. The calculated electron excitation transfer constants between N₂(A ³Σ _u ⁺ , v = 1, 0) and Zn(¹ S) over the temperature range 300–900 K were on the order of 10^?11?10^?12 cm³/s.     

Theoretical studies on 14 Λ-S and 30 Ω states of BeBr molecule: potential energy curves,spectroscopic parameters and spin–orbit couplings

Using the complete active space self-consistent field (CASSCF) method followed by the internally contracted multi-reference configuration interaction (MRCI) approach in combination with the correlation-consistent basis sets, this paper studies the potential energy curves of X²Σ⁺, 2²Σ⁺, 3²Σ⁺, 1²Σ^?, A²Π, 2²Π, 3²Π, 1²Δ, 1⁴Σ⁺, 2⁴Σ⁺, 1⁴Σ^?, 1⁴Π, 2⁴Π and 1⁴Δ Λ-S states of BeBr molecule and the corresponding 30 Ω states for the first time. All the Λ-S states correlate to the first two dissociation channels, Be(¹S_g) + Br(²P_u) and Be(³P_u) + Br(²P_u), of BeBr molecule. Of these Λ-S states, the 3²Π and 2⁴Π are found to be repulsive without the spin–orbit coupling, whereas 1⁴Π, 2⁴Π, 3²Π and 2⁴Σ⁺ are found to be repulsive with the spin–orbit coupling included. A²Π and 2²Σ⁺ possess the double well whether the spin–orbit coupling effect is included or not. Only 1⁴Σ⁺, 1⁴Σ^?, 1²Π and 2²Π are found to be the inverted Λ-S states. The spin–orbit coupling is accounted for by the state interaction approach with Breit–Pauli Hamiltonian using the all-electron cc-pCVTZ basis set. The potential energy curves determined by the internally contracted MRCI method are corrected for size-extensivity errors by means of the Davidson correction. Core–valence correlation correction is calculated with a cc-pCVTZ basis set. Scalar relativistic correction is included using the third-order Douglas–Kroll Hamiltonian approximation at the level of cc-pVTZ basis set. The spectroscopic parameters of all the Λ-S and Ω bound states are evaluated. The spectroscopic parameters are compared with those reported in the literature. Fair agreement is found between the present results and available measurements. In particular, the energy splitting of 204.43 cm^?1 in the A²Π Λ-S state agrees well with the measurements of 201 cm^?1. Analyses demonstrate that the spectroscopic parameters reported here can be expected to be reliably predicted ones.     

Deperturbation of the N2+ first negative group B2Σu+-X2Σg+

Twelve bands of the N₂⁺B²Σ_u⁺-X²Σ_g⁺ system, including v_B = 0–6 and v_X = 0–8, are reanalyzed. All effects of B²Σ_u⁺ ～ A²Π_u perturbations are explicitly considered. Despite the use of high precision (0.01 cm^?1) line measurements, no evidence for a perturber other than A²Π_u is obtained. Deperturbed constants for the B²Σ_u⁺ and X²Σ_g⁺ states are derived. The deperturbation is shown to be self-consistent and complete (excluding effects of the C²Σ_u⁺ state) by examining semiempirical relationships of the perturbation matrix elements with the spin-rotation constants of the B and X states and atomic spin-orbit parameters. A number of previous analyses of transitions involving the v_B = 3 and 5 levels are found to be incorrect.     

Perturbations in the A1Π, v = 0 state of 12C18O investigated via complementary spectroscopic techniques

The A¹Π(v = 0) level of ¹²C¹⁸O has been reinvestigated using three different high-resolution spectroscopic methods: (1) 2 + 1′ resonance-enhanced multiphoton ionisation of the A¹Π ? X¹Σ⁺(0, 0) band using narrowband lasers in a Doppler-free geometry; (2) Fourier-transform emission spectroscopy in the visible range probing the B¹Σ⁺ ? A¹Π(0, 0) band in a discharge; (3) Fourier-transform absorption spectroscopy in the vacuum-ultraviolet range measuring the A¹Π ? X¹Σ⁺(0, 0) and B¹Σ⁺ ? X¹Σ⁺(0, 0) bands at multiple temperatures ranging from 90 to 900 K. An effective-Hamiltonian analysis of A¹Π, v = 0 levels was performed up to J = 44 which quantitatively addresses perturbations by the e?³Σ^?(v = 1), d³Δ(v = 4), a′³Σ⁺(v = 9), D?¹Δ(v = 0), and I?¹Σ^?(v = 0, 1) levels.     

Spectroscopic studies of the sulphur afterglow

The afterglow emission spectrum of sulphur and argon mixture is found to consist of (a) the main band system of S₂(B³Σ^-_u?X³Σ^-_g) in the region 3200–6600 Å and (b) the atomic spectrum of argon in the 7500–9000 Å region. Although B?X bands of S₂ obtained by ordinary excitation extends from 2829 to 7100 Å, the lower wavelength limit of these bands from the afterglow is only 3200Å. It is proposed that the S₂ molecules are formed in the B³Σ^-_u state through inverse predissociation when two S atoms approach each other along the potential curve of the predissociating electronic state 1_u.     

EPR of Mn2+ doping unannealed single crystal of (La2O3)0.95(CeO2)0.05

X-band room temperature EPR spectra have been recorded for Mn²⁺ ion doping unannealed (La₂O₃)_0.95(CeO₂)_0.05 host crystal. The data are analysed using a rigorous least-squares fitting procedure in which a large number of lines characterized by ΔM = ± 1, Δm = 0 transition, obtained for several orientations of the static magnetic field, are simultaneously fitted. Combined with the knowledge of the absolute sign of the hyperfine interaction parameter. A, the hyperfine Hamiltonian parameters A, B, Q as reported in this paper, are given with their correct signs. The information on the linewidth is used to deduce the deviation of the crystal-field axes of different Mn²⁺ ions from the c axis; on the basis of the model proposed here these deviations are found to be between 0 and 10°.     

The Hg2 (A3Ou− → X1Σg+) and (A31u → X1Σg+) fluorescence

The fine structure emission sepctrum near 5500 Å attributed to the Hg₂ (A³O_u^? → X¹Σ_g⁺) transition is shown to be strikingly similar to the HgCl (B²Σ⁺ → X²Σ⁺) emission spectrum sensitized by Hg(6³P_o) metastables. The correct Hg₂ (A³O_u^? → X¹Σ_g⁺) emission spectrum at 4850 Å was re-examined and confirmed to be a continuous one. It is suggested that the fine structure arose from the sensitization of a chlorine containing impurity.