Ivan O. Antonov

Spectroscopic investigations of ThF and ThF

The electronic spectra of ThF and ThF(+) have been examined using laser induced fluorescence and resonant two-photon ionization techniques. The results from high-level ab initio calculations have been used to guide the assignment of these data. Spectra for ThF show that the molecule has an X (2)Δ(3/2) ground state. The upper spin-orbit component, X (2)Δ(5/2) was found at an energy of 2575(15) cm(-1). The low-lying states of ThF(+) were probed using dispersed fluorescence and pulsed field ionization-zero kinetic energy (PFI-ZEKE) photoelectron spectroscopy. Vibronic progressions belonging to four electronic states were identified. The lowest energy states were clearly (1)Σ(+) and (3)Δ(1). Although the energy ordering could not be rigorously determined, the evidence favors assignment of (1)Σ(+) as the ground state. The (3)Δ(1) state, of interest for investigation of the electron electric dipole moment, is just 315.0(5) cm(-1) above the ground state. The PFI-ZEKE measurements for ThF yielded an ionization energy of 51 581(3) cm(-1). Molecular constants show that the vibrational constant increases and the bond length shortens on ionization. This is consistent with removal of a non-bonding Th-centered 6d or 7s electron. Laser excitation of ThF(+) was used to probe electronically excited states in the range of 19,000-21,500 cm(-1).

Experimental and theoretical study of distribution of O2 molecules over vibrational levels in O2(a 1Δg)–I mixture

The vibrationally excited oxygen in O2(a 1Δg)–I mixture was detected by emission spectroscopy. The analysis of a luminescence spectra of oxygen molecules on O2(b 1Σg+,v′)→O2(X 3Σg−,v″) transitions has shown that vibrationally excited O2(b 1Σg+) molecules up to v=5 are generated in the active medium of chemical oxygen–iodine laser (COIL). The highest values of relative O2(b 1Σg+,v=1) population of 22±2% and O2(b 1Σg+,v=2) of 10±3.5% are reached for I2 content in an oxygen flow ≈1%. It is shown theoretically that the relative populations of O2(X 3Σg−), O2(a 1Δg), and O2(b 1Σg+) molecules at the first and the second vibrational levels are approximately equal because of fast EE energy exchange between oxygen molecules. Up to 20% of oxygen molecules in COIL active medium are vibrationally excited. Comparison of intensities of O2(b 1Σg+,v′)→O2(X 3Σg−,v″) bands has demonstrated that a few percent of O2(b 1Σg+,v) molecules are vibrationally excited with v=3, 4, or 5. It is suggested that the following pooling rea...

Spectroscopy and Structure of the Simplest Actinide Bonds

Understanding the influence of electrons in partially filled f- and d-orbitals on bonding and reactivity is a key issue for actinide chemistry. This question can be investigated by using a combination of well-defined experimental measurements and theoretical calculations. Gas phase spectroscopic data are particularly valuable for the evaluation of theoretical models. Consequently, the primary objectives of our research have been to obtain gas phase spectra for small actinide molecules. To complement the experimental effort, we are investigating the potential for using relativistic ab initio calculations and semiempirical models to predict and interpret the electronic energy level patterns for f-element compounds. Multiple resonance spectroscopy and jet cooling techniques have been used to unravel the complex electronic spectra of Th and U compounds. Recent results for fluorides, sulfides, and nitrides are discussed.

Spectroscopic and theoretical investigations of UF and UF

Laser induced fluorescence and resonantly enhanced multiphoton ionization spectra were recorded for UF in the 18,000-20,000 cm(-1) range. Rotationally resolved data were obtained, and the analysis of a band at 18624 cm(-1) yielded a ground state rotational constant of 0.2348 cm(-1). The electronic ground state was clearly identified as |Ω| = 4.5, confirming the theoretically predicted U(+)(5f(3)7s(2))F(-) configuration. Dispersed fluorescence spectra revealed low-lying electronic states that are assigned as |Ω| = 3.5 (435 cm(-1)) and 2.5 (650 cm(-1)). Two-color photoionization spectroscopy was used to study UF(+). The ground state and fifteen electronically excited states have been characterized. The ground state was found to be |Ω| = 4, as it is for the isoelectronic molecule UO, and with vibrational constants of ωe = 649.92 and ωexe = 1.83 cm(-1). The patterns of electronically excited states observed for UF(+), with |Ω| values ranging from 0 to 6, were qualitatively consistent with the predictions of a ligand field theory model developed for UO. The experimental data for both UF and UF(+) were reasonably well reproduced by CASSCF/CASPT2 electronic structure calculations that included spin-orbit coupling.

Detection of vibrationally excited O2 in O2(a1Δg)–I mixture

Abstract The vibrationally excited oxygen in the O 2 (a 1 Δ g )–I mixture by emission spectroscopy was detected. The analysis of a luminescence spectra of oxygen molecules on the O 2 (b 1 Σ g + , v = i )→O 2 (X 3 Σ g − , v ′ = i ) transitions ( i =0,1,2) has shown, that ≈22% of O 2 (b 1 Σ g + ) molecules are excited with v =1 and ≈10% with v =2. It is shown theoretically, that a mean number of vibrational quanta per one molecule in each of components O 2 (X 3 Σ g − ), O 2 (a 1 Δ g ) and O 2 (b 1 Σ g + ) is approximately equal because of fast EE energy exchange between oxygen molecules and reaches 0.3.

Experimental and theoretical studies of the electronic transitions of BeC

Electronic spectra for BeC have been recorded over the range 30,500-40,000 cm(-1). Laser ablation and jet-cooling techniques were used to obtain rotationally resolved data. The vibronic structure consists of a series of bands with erratic energy spacings. Two-color photoionization threshold measurements were used to show that the majority of these features originated from the ground state zero-point level. The rotational structures were consistent with the bands of (3)Π-X(3)Σ(-) transitions. Theoretical calculations indicate that the erratic vibronic structure results from strong interactions between the four lowest energy (3)Π states. Adiabatic potential energy curves were obtained from dynamically weighted MRCI calculations. Diabatic potentials and coupling matrix elements were then reconstructed from these results, and used to compute the vibronic energy levels for the four interacting (3)Π states. The predictions were sufficiently close to the observed structure to permit partial assignment of the spectra. Bands originating from the low-lying 1(5)Σ(-) state were also identified, yielding a (5)Σ(-) to X(3)Σ(-) energy interval of 2302 ± 80 cm(-1) and molecular constants for the 1(5)Π state. The ionization energy of BeC was found to be 70,779(40) cm(-1).

Chemical oxygen-iodine laser with CO2 buffer gas

The efficient power operation in a chemical oxygen-iodine laser for subsonic and supersonic modes has been demonstrated. It is shown that the substitution of the buffer gas N2 by CO2 does not cause any significant variation in the dependence of the output power on the degree of dilution of the active medium. The maximum power was 581W for the flow rate of molecular chlorine 22mMol∕s that corresponds to a chemical efficiency of ηchem=29%.

Spectroscopic and Theoretical Investigations of ThS and ThS

Gas-phase ThS has been produced via the reaction of laser ablated Th with H2S. Rotationally resolved electronic spectra were recorded by laser-induced fluorescence (LIF) over the range 17500-24000 cm(-1). Resonance-enhanced multiphoton ionization was used in conjunction with a time-of-flight mass spectrometer to confirm the assignments of nine LIF bands to ThS. Using excitation of a ThS band centered at 22118 cm(-1), a dispersed fluorescence spectrum revealed a vibrational progression of the X(1)Σ(+) ground electronic state and the term energies of two low-lying excited states ((3)Δ1 and (3)Δ2). Two-color photoionization spectroscopy was used to study ThS(+). An accurate ionization energy for ThS was obtained (54425(3) cm(-1)); ThS(+) vibronic term energies up to v = 7 in the X(2)Σ(+) ground state and v = 3 in the (2)Δ3/2 first excited state were recorded. High-level electronic structure calculations, with inclusion of the spin-orbit interactions yielded predictions that were in good agreement with the experimental data for ThS and ThS(+). The spectroscopic properties of ThS/ThS(+) are compared with those of the valence isoelectronic pairs ThO/ThO(+), HfO/HfO(+), and HfS/HfS(+).

Formation of I2(B3Π0) in the presence of O2(a1Δ)

The mechanism by which I2(B3Π0) is excited in the chemical oxygen-iodine laser was studied by means of emission spectroscopy. Using the intensity of the O2(b1Σ,υ′=0)→O2(X3Σ,υ″=0) band as a reference, I2(B3Π0) relative number densities were assessed by measuring the I2(B3Π0,υ′)→I2(X1Σ,υ″) emission intensities. Vibrationally excited singlet oxygen molecules O2(a1Δ,υ′=1) were detected using infrared emission spectroscopy. The measured relative density of O2(a1Δ,υ′=1) for the conditions of a typical oxygen-iodine laser medium amounted to ∼15% of the total O2(a1Δ) content. Mechanisms for I2(B3Π0) formation were proposed for both the I2 dissociation zone and the region downstream of the dissociation zone. Both pumping mechanisms involved electronically excited molecular iodine I2(A′3Π2u, A3Π1u) as an intermediate. It is proposed that in the dissociation zone the molecular iodine A′3Π2u and A3Π1u states are populated in collisions with vibrationally excited singlet oxygen molecules O2(a1Δ,υ′), whereas in the dow...