MRD CI study on the low-lying states of AlP

Large-scale MRD CI calculations assign to AlP the ground state X ³Σ⁻ (9σ²3π²) and a close-lying state 1 ³Π (9σ3π³) (T_e = 0.08 eV). Up to transition energies of 2.0 eV, other states are described by the configurations 9σ3π³ (1¹Π), 8σ²3π⁴ (1 ¹Σ⁺), 9σ²3π² (1 ¹Δ and 2 ¹Σ⁺) and 9σ3π²4π (1 ⁵Π). The 2 ³Π state, located at ≈ 2.30 eV, shows a shallow double minimum. Numerous perturbations are expected to induce predissociation upon 2 ³Π. Multiplets arising from the occupation 8σ²3π³4π are clustered in the 3.25–3.50 eV region. Quintet states with the configuration 8σ9σ3π³4π are bound, with T_e values (in eV) of 3.80 (1 ⁵Σ⁺), 4.44 (1 ⁵Δ) and 4.88 (3 ⁵Σ⁻), respectively. The 9σ → 4s Rydberg members ⁵Σ⁻ and ³Σ⁻ lie in the 4.58–4.72 eV energy region. The first ionization potential (ionization to X⁴Σ⁻ of AlP⁺, 9σ → ∞) is estimated to be 7.65 eV. Ionization to the 1 ²Σ⁻ and 1 ²Π states of AlP⁺ is suggested to occur between 8.0 and 8.8 eV. The dipole moments of X ³Σ⁻, 1 ¹Δ and 2 ¹Σ⁺ are close to 1.0 D, whereas the 1 ¹Σ⁺ state has μ = 3.49 D; 1 ³Π and 1 ¹Π have dipole moments from 2.45 to 2.91 D. All low-lying states show a polarity Al⁺P⁻. Finally, the electronic structure and transition energies of AlP are compared with those of the isoelectronic species BN, AIN, and SiP⁺.     

Identification of a new progression of the Cl2 molecule with Σu symmetry

Synchrotron radiation is used to excite selectively the chlorine molecule in a Ne buffer gas. Due to the fast relaxation induced by the buffer gas, in the excitation spectrum of the D′→A′ emission at 258 nm, a new progression is observed. It is attributed to the 3 ¹Σ_u⁺ state which is the result of an avoided crossing between the Rydberg state π_g→5pπ and the valence state (1441) (σ_g→σ_u). It is characterized by T_e=83251 cm⁻¹, ω_e=783 cm⁻¹, ω_ex_e=29.6 cm⁻¹ and r_e=1.844 Å.     

Electronic structure of the radicals NF and NCl. III. The radiative lifetimes of the bΣ and aΔ states

The radiative lifetimes of the b¹Σ⁺ and a¹Δ states have been evaluated by perturbation expansions including X³Σ⁻, a¹Δ, b¹Σ⁺, 1^3,1Π, 2^3,1Π, 2³Σ⁻ and 2¹Σ⁺ states. All wavefunctions result from large MRD CI calculations. The b—X transition is dominated by the parallel transition moment; it is found to be much stronger than the a—X transition. The calculated radiative lifetimes of τ(¹Σ⁺)=18 ms, τ(¹Δ)=2.2 s for NF and τ(¹Σ⁺)=2.5–3.5 ms for NCl are in good accord with corresponding experimentally deduced values. The lifetime for the a¹Δ state in NCl is found to be τ(¹Δ)=1.1 s, ie. much longer than derived from a recent experiment. Its magnitude is consistent with the τ(b¹Σ⁺)/τ(a¹Δ) ratio of similar systems and with the decrease in lifetime from NF to NCl and is thus believed to be quite reliable. A detailed analysis of all contributions of the perturber states to the transition mechanism is made and comparison with the related data in SO, O₂ and S₂ is undertaken. The b-a transition probability dominated by the quadrupole transition is fairly constant in all the systems in the order of A = 0.013 (NF) - 0.0013 (S₂) s⁻¹.     

A new singlet state of Te2

The 4067 Å line of the krypton-ion laser covers two transitions in the BO⁺_u-X O⁺_g system of ¹³⁰Te₂, R(36) in the 16-0 band and R(172) in the 18-0 band. Subsequent fluorescence has been recorded by Fourier transform spectrometry in the range 5900 to 15000 cm⁻¹. Many transitions, with v' in the range 0 to 47, have been assigned to a new system, B O⁺_u-b¹ ∑⁺_g, and vibrational and rotational constants for the new state have been derived. The value of T_e for b ^I∑_g⁺ is about 9600.2 cm⁻¹.     

Simultaneous derivative spectrophotometric determination of thorium and uranium in a micellar medium

Derivative photometric methods for trace analysis of Th(IV) and UO₂(II), and their simultaneous determination in mixtures using 5,8-dihydroxy-1,4-naphthoquinone in a micellar medium are reported. Molar absorptivity and Sandell's sensitivity of 1:2 Th(IV) and 1:1 UO₂(II) complexes at their λ_max, 614.5 nm and 637.0 nm are, 1.19 × 10⁴ 1/mol/cm and 1.12 × 10⁴ 1/mol/cm and 1.95 × 10⁻² μg/cm² and 2.13 × 10⁻² μg/cm² μg/cm², respectively. Calibration graph is linear over the range 9.28 × 10⁻²−18.56 μg/ml of Th(IV) and 9.52 × 10⁻²−19.04 μg/ml of UO₂(II). Though presence of Th(IV) and UO₂(II) causes interference in each others determination, 9.28 × 10⁻¹−9.28 μg/ml Th(IV) and 9.52 × 10⁻¹−9.52 μg/ml UO₂(II) when present together, can be simultaneously determined using derivative spectra.     

Lifetime measurements of electronically excited C3(Πu) radicals in different vibrational states

The radiative lifetimes of nine vibrational levels of the C₃(¹Π_u) radical were obtained from decay time studies of the C₃(¹Π_u → ¹Σ⁺_g) fluorescence induced by a tunable dye laser. The lifetimes of the different vibronic levels were found to be constant within the experimental error limits, namely, τ_o = (200 ± 10) ns. The collisional deactivation of the C₃(¹Π_u) states by helium gives rate constants between 2.5 and 4 in 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ units.     

Kinetic investigation of electronic energy transfer processes following the pulsed dye-laser generation of excited atomic barium, Ba[6s6p(P1)], in the presence of atomic strontium

The collisional behaviour of Ba[6s5d(³D_J)], 1.151 eV above the 6s²(¹S₀) electronic ground state, in the presence of atomic strontium, has been investigated in the ‘long-time domain' (ca. 100 μs–1 ms) following the pulsed dye-laser excitation of barium vapour at elevated temperature at λ = 553.5 nm (Ba[6s6p(¹P₁)] ← Ba[6s²(¹S₀)]. Ba(³D_J) is subsequently produced from the short-lived ¹P₁ state (τ_e = 8.37 ± 0.38 ns) by a number of radiative and collisional processes. It may then be monitored in the ‘long-time domain' by atomic spectroscopic marker methods involving either collisional activation of Ba(³D_J) by Ba(¹S₀) and He buffer gas to yield Ba[6s6p(³P_J)] with subsequent emission from the ³P₁ state (τ_e = 1.2 ± 0.1 μs): Ba[6s6p(³P₁)] → Ba[6s²(¹S₀)] + hv (λ = 791.1 nm). Alternatively, emission from Ba(¹P₁) may be monitored at long times following the generation of this short-lived state by energy pooling following self-annihilation of Ba(³D_J) + Ba(³D_J) from Ba[6s6p(¹P₁)] → Ba[6s²(¹S₀)] + hv (λ = 553.5 nm). The generation of Ba(³D_J) in the presence of atomic strontium yields emission in the long-time domain from Sr[5s5p(³P₁)] (τ_e = 19.6 μs): Sr[5s5p(³P₁)] → Sr[5s²(¹S₀)]  + hv (λ = 689.3 nm). Whilst the decay profiles at short times are complex in form, at long times all these atomic profiles show first-order kinetic removal with the decay coefficients for λ = 791.1 nm, 689.3 nm and 553.5 nm emissions in the ratio 1 : 2 : 2, consistent with overall third-order activation of the form: Ba(³D_J) + Ba(³D_J) + Sr(¹S₀) → Sr(³P_J) + 2Ba(¹S₀). The mechanism is modelled in detail, including measurement of integrated emission intensities, yielding kinetic data for fundamental collisional processes. The overall rate constant for the third-order collisional activation of Sr[5s5p(³P_J])from 2Ba[6s5d(³D_J)] + Sr[5s²(¹S₀)] takes the upper limit of 5.8 × 10⁻²⁷ cm⁶ atom⁻² s⁻¹ (T = 900 K). The rate constant for the two body collisional quenching of Ba[6s5d(³D_J)] by ground state atomic strontium, Sr[5s²(¹S₀)], is found to be (2.0 ± 0.1) × 10⁻¹² cm³ atom⁻¹ s⁻¹ (T = 900 K).     

Photodissociation spectroscopy of Mg—Ar

Mg⁺—Ar ion—molecule complexes are produced in a pulsed supersonic nozzle cluster source. The complexes are mass selected and studied with laser photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer system. An electronic transition assigned as X ²Σ⁺ → ²Π is observed with an origin at 31387 cm⁻¹ (vac) for ²⁴Mg⁺—Ar. The ²⁴Mg⁺—Ar spectrum is characterized by a 15 member progression with a frequency (ω′_e) of 272 cm⁻¹. An extrapolation of this progression fixes the excited state dissociation energy (D′_o) at 5552 cm⁻¹. The corresponding ground-state value (D″_o) is 1270 cm⁻¹ (3.6 kcal/mol). The ²Π _, spin—orbit splitting is 76 cm⁻.     

The potential energy function for the ground state of CCl calculated from spectroscopic data

The dissociation energy (D_e= 57754±872 cm⁻¹ has been estimated for the ground state of CCl⁺ by fitting a Hulburt-Hirschfelder potential to the RKR turning points. This value of D_e has been used together with molecular constants B_e, ω_e, a_i (i= 1–6) and R_e obtained by Gruebele and co-workers to construct a potential energy function for CCl⁺ in the form of a perturbed Morse oscillator.     

A quantum mechanical analysis on the selective production of the oxygen atom fine-structure states along asymmetric resonances in OH predissociation

Predissociation of the A ²Σ⁺ state is treated by an exact theory employing two frame transformation matrices, each of which connects the atomic term limits (O(³P) and O(¹D)) to the correlating adiabatic Born—Oppenheimer states. Resonances corresponding to the higher (v 7) rovibrational levels of the A ²Σ⁺ state are predicted to have asymmetric (Fano-type) profiles. The branching ratios of O(³P_j, J = 0, 1, 2) are shown to be influenced by nonadiabatic interactions in the Franck—Condon region between the A ²Σ⁺ and dissociative ⁴Σ⁻, ²Σ⁻ and ⁴Π states. The branching ratios show a strong variation along asymmetric resonances, while remaining energy independent along Lorentzian resonances.     

Transition state spectroscopy of open shell systems: Angle-resolved photodetachment spectra for the adiabatic singlet states of OHF

In this work three-dimensional potential energy surfaces of the first five singlet states of OHF are developed based on fits of more than 10,000 highly accurate ab initio points. An approximate treatment is presented for the calculation of the anisotropy parameter describing the electron angular distribution photodetached from a molecular anion. This method is used to calculate the angle-resolved photoelectron spectra in the photodetachment of OHF⁻. The wave packet formed in the neutral OHF system is placed at the transition state region, and yields the formation of OH + F and HF + O products. The results are compared with the recent experimental measurements published by Neumark [D.M. Neumark, Phys. Chem. Chem. Phys. 7 (2005) 433]. The intensity found at low electron kinetic energy including these five states and the three lower triplet states is found to be low. To analyze the effect of higher electronic states more excited ¹Σ⁻, ³Σ⁺ and ³Δ states are calculated at collinear geometry. The agreement with the experimental data improves, thus demonstrating that the correct simulation of the photodetachment spectrum at 213 nm involves at least 12 electronic states. All the structures of the experimental spectra are semiquantitatively reproduced finding an overall good agreement. It is concluded that the main problem of the simulation is in the intensity and anisotropy parameters. An alternative to their calculation would be to fit their values to reproduce the experimental results, but this would require to separate the contribution arising from different final electronic states.     

The A Πu-X Πg emission spectrum of I2

The A ²Π_u-X ²Π_g electronic emission spectrum of I₂⁺ has been recorded at a low rotational temperature in a crossed molecular beam/electron beam apparatus. Six vibrational sequences with five or more members have been assigned to progressions in ν′, giving ω′_e = 122±8 cm⁻¹, but a full vibrational analysis has not been possible. It is not known whether this is due to the relatively poor resolution (≈5 cm⁻¹) at which the spectrum has been recorded or because the A ²Π_u state is perturbed in one or both spin-orbit components. Existing data on the A state of I₂⁺ are reviewed.     

On the 6Πu state of Na2

The 6¹Π_u state of sodium dimer has been observed up to v = 53 in excitation spectra of the system, recorded by polarisation labelling spectroscopy technique. The Dunham coefficients are derived and the potential energy curve constructed by the inverted perturbation approach method. Equilibrium constants for the 6¹Π_u state of Na₂ are: T_e = 35446.06 ± 0.04 cm⁻¹ (with respect to the minimum of the electronic ground state), Y₁₀ = 111.388 ± 0.019 cm⁻¹, Y₀₁ = 0.112122 ± 0.000017 cm⁻¹.     

The chemical production of electronically excited states in the H/NF2 system

A mixture of NF₃ and Ar is passed through an rf discharge in a flow-system to produce, among other species, F and NF₂. When H₂, D₂, or CH₄ are added downstream, reactions with F atoms produce vibrationally excited HF or DF together with H, D, or CH₃. The latter free radicals can react with NF₂, probably by an elimination reaction to produce electronically excited NF: NF₂(²B₁) + H(D, CH₃) → HF^*(DF^* + NF(a¹Δ). A vibrational-to-electronic energy transfer process between the products of this reaction then produces the next higher state of NF: HF(ν 2) + NF(a¹Δ) → HF(ν−2) + NF(b¹Σ⁺). A similar transfer process has also been found between the electronically excited a¹Δ states of O₂ and NF: O₂(a¹Δ) + NF(a¹Δ) → O₂(X³Σ⁻) + NF(b¹Σ⁺). The H or D atoms but not the CH₃ radicals are then found to react with either NF(a¹Δ) or NF(X³Σ⁻) to produce electronically excited N(₂D) atoms, which in turn react with the NF(a¹Δ) molecules to produce N₂(B³Π_g). The observed nitrogen first positive radiation has been demonstrated to be produced entirely by this reaction mechanism rather than by the N(⁴S) recombination that accounts for the Rayleigh afterglow. In addition, the occurrence of the reaction N(₂D) + N₂O → NO(B²Π_r) + N₂ (X¹Σ⁺_g) has been verified. Finally we have observed emission at 3344 Å, which we attribute to the NF(A³Π), which has not been previously reported.     

Autoionization spectra of Li2 and the XΣg ground state of Li2: Experimental and theoretical investigations

Autoionizing Rydberg levels of Li₂ molecules in a supersonic molecular beam are populated by stepwise excitation with two tunable pulsed dye lasers. The observed autoionization spectra show severe perturbations. Based on calculations of quantum defects and a perturbation treatment of l-uncoupling a tentative assignment of Rydberg series up to n = 32 is proposed. The convergence limits of these series yield a value of IP = 41475 cm⁻¹ for the adiabatic ionization potential and a vibrational constant ω_e = 263 cm⁻¹ for the X²Σ⁺_g ground state of Li⁺₂. The experimental results are compared with ab initio calculations combined with a core polarization potential, which yield the potential curve. the dissociation energy, the quadrupole moment and the vibrational frequency for the X²Σ⁺_g ground state of Li⁺₂, in the excellent agreement with experimental findings.     

Fraction of excited-state oxygen formed as b Σg in solution-phase-photosensitized reactions II. Effects of sensitizer substituent

The fraction F_Σ of excited-state oxygen formed as b ¹Σ_g⁺ was determined for a series of triplet-state photosensitizers in CCl₄ solutions. F_Σ was determined by monitoring the intensities of (a) O₂(b ¹Σ_g⁺) fluorescence at 1926 nm (O₂(b ¹Σ_g⁺)→O₂(a ¹Δ_g) and (b) O₂(a ¹ Δ_g) phosphorescence at 1270 nm (O₂(a ¹Δ_g) → O₂(X³Σ_g⁻)). Oxygen excited states were formed by energy transfer from substituted benzophenones and acetophenones. The data indicate that F_Σ depends on several variables including the orbital configuration of the lowest triplet state and the triplet-state energy. The available data indicate that the sensitizer-oxygen charge transfer (CT) state is not likely to influence F_Σ strongly by CT-mediated mixing of various sensitizer-oxygen states.     

Ab initio calculations on the multipole moments and dipole polarisabilities of the PO molecular ion (XΣ)

The potential energy, dipole, quadrupole and octopole moments and dipole polarisabilities have been calculated at CASSCF level for the ground X¹Σ⁺ state of the PO⁺ molecular ion as a function of internuclear distance. Most of the electrical properties have not previously been calculated and show rapid variations around 5 a.u. due to a perturbation. The calculated vibrational frequency of 1410.4 cm⁻¹ and the integrated IR absorption intensity of 984 cm² mol⁻¹ should lead towards the first observation of the vibrational spectrum.     

Millimeter-wave rotational spectrum and molecular constants of diatomic gallium iodide

The gas-phase molecular spectrum of Gal has been detected in the millimeter wavelength region. The molecules are produced by vapourising a mixture of gallium and lead iodide into an evaculated cell. Analysis of the observed rotational transitions yields the following molecular parameters for ⁶⁹Ga¹²⁷I: Y₀₁ = 1706.89645(83) MHz, Y₁₁ = −5.68714(53) MHz, Y₂₁ = 6.329(43) kHz, Y₀₂ = −0.472713(60) kHz, Y₁₂ = 0.472(38) Hz, ω_e = 216.38 cm⁻¹, ω_e^x_e= 0.471 cm⁻¹, and for ⁷¹Ga¹²⁷I: y₀₁ = 1675.72004(71) MHz, Y₁₁ = −5.53277(57) MHz, Y₂₁ = 5.995(34) kHz, Y₀₂ = −0.455700(51) kHz, y₁₂ = 0.522(40) Hz, ω_e = 214.37 cm⁻¹, and ω_e^x_e = 0.458 cm⁻¹. The equilibrium internuclear distance obtained for Gal is r_e = 2.574667(12) Å.     

First observation of the 3Π and 4Π states of NaLi molecule

Two previously unknown electronic states of NaLi molecule have been observed by polarisation labelling spectroscopy in the energy region of 29 900–34 100 cm⁻¹ above the bottom of the molecular ground state potential well. The states are identified as 3¹Π(Na(3d) + Li(2s)) and 4¹Π(Na(4p) + Li(2s)). The Dunham coefficients are derived for both states and the potential energy curves constructed by the Rydberg–Klein–Rees method.     

Quenching of the translationally hot and thermalized NH(c Π) radicals by HN3

The cross section for the quenching of NH(c ¹Π, ν = 0) by HN₃ was measured by using a pulsed laser technique. A single rotational level of NH(c ¹Π, ν = 0) was formed by exciting NH(a ¹Δ, ν = 0) with a frequency doubled dye laser. NH(a¹Δ) was produced by photolyzing HN₃ with a XeCl excimer laser. The time profiles of the NH(c-a) fluorescence were measured at various pressures of HN₃. Experiments were performed both in the presence and in the absence of He buffer gas. In the absence of He, the NH radicals were found to be translationally hot; the average velocity was 3800±600 m s⁻¹. The quenching cross sections for the translationally hot and thermalized NH(c) radicals by HN₃ were determined to be (28±5) × 10⁻¹⁶ and (85±3) × 10⁻¹⁶ cm², respectively. No rotational level dependence could be observed in the quenching of the hot NH(c) radicals.