High resolution analysis of the ν7 and ν9 bands of DCOOH

The 7¹ and 9¹ vibrational states of deuterated species of formic acid molecule DCOOH have been recorded by a FTIR spectrometer in the region 450- at a resolution of and a millimeter wave spectrometer. In the analysis microwave transitions from literature were used in addition to 14 835 assigned IR and 114 millimeter wave lines in the 7¹ and 9¹ vibrational states. The analysis resulted in band origins, rotational, centrifugal distortion, and eight interaction parameters of the Coriolis coupled 7¹ and 9¹ vibrational states. RMS deviation of the fit was for the IR data and the maximum values of J and K_a quantum numbers in the fit were 64, 28 and 64, 30 for 7¹ and 9¹ states, respectively.     

Modification of the Robert-Bonamy formalism in calculating Lorentzian half-widths and shifts

We have found an invalid assumption in the Robert-Bonamy formalism that has been widely used for calculating Lorentzian spectral line half-widths and shifts for decades. The problem results in their derivation where they assumed the cumulant expansion can be used to evaluate the Liouville matrix element . At first sight, their assumption appears to be correct because this matrix element is diagonal in the Liouville space and as a result, it looks like that a basic requirement in applying the cumulant expansion is satisfied. However, by decomposing it into two Hilbert matrix elements associated with S_I and S_F, respectively, we have found that neither of these is diagonal in Hilbert space. Therefore, their assumption is not valid and their expressions for the half-widths and shifts are incorrect. We have found by choosing an average over the internal degrees of the bath molecule as the average in the cumulant expansion, one is able to apply this expansion properly and obtain the correct expressions. Numerical calculations show new half-width and shift values differ from previous ones, and the stronger the interaction between two molecules is, the larger these differences are.     

Stretch-bend combination polyads in the ÃAu state of acetylene, C2H2

Rotational analyses are reported for a number of newly-discovered vibrational levels of the S₁-trans (ùA_u) state of C₂H₂. These levels are combinations where the Franck-Condon active and vibrational modes are excited together with the low-lying bending vibrations, and . The structures of the bands are complicated by strong a- and b-axis Coriolis coupling, as well as Darling-Dennison resonance for those bands that involve overtones of the bending vibrations. The most interesting result is the strong anharmonicity in the combinations of (trans bend, a_g) and (in-plane cis bend, b_u). This anharmonicity presumably represents the approach of the molecule to the trans-cis isomerization barrier, where ab initio results have predicted the transition state to be half-linear, corresponding to simultaneous excitation of and . The anharmonicity also causes difficulty in the least squares fitting of some of the polyads, because the simple model of Coriolis coupling and Darling-Dennison resonance starts to break down. The effective Darling-Dennison parameter, K₄₄₆₆, is found to increase rapidly with excitation of , while many small centrifugal distortion terms have had to be included in the least squares fits in order to reproduce the rotational structure correctly. Fermi resonances become important where the K-structures of different polyads overlap, as happens with the 2¹3¹B¹ and 3¹B³ polyads (B = 4 or 6). The aim of this work is to establish the detailed vibrational level structure of the S₁-trans state in order to search for possible S₁-cis (¹A₂) levels. This work, along with results from other workers, identifies at least one K sub-level of every single vibrational level expected up to a vibrational energy of 3500 cm⁻¹.     

Laser excitation spectrum of C3 in the region 26 000-30 700 cm

The vibrational structure of the electronic state of C₃ in the region 26 000-30 775 cm⁻¹ has been re-examined, using laser excitation spectra of jet-cooled molecules. Rotational constants and vibrational energies have been determined for over 60 previously-unreported vibronic levels; a number of other levels have been re-assigned. The vibrational structure is complicated by interactions between levels of the upper and lower Born-Oppenheimer components of the state, and by the effects of the double minimum potential in the Q₃ coordinate, recognized by Izuha and Yamanouchi [16]. The present work shows that there is also strong anharmonic resonance between the overtones of the ν₁ and ν₃ vibrations. For instance, the levels 2 1⁺ 1 and 0 1 ⁺ 3 are nearly degenerate in zero order, but as a result of the resonance they give rise to two levels 139 cm⁻¹ apart, centered about the expected position of the 2 1⁺ 1 level. With these irregularities recognized, every observed vibrational level up to 30 000 cm⁻¹ (a vibrational energy of over 5000 cm⁻¹) can now be assigned. A vibronic level at 30181.4 cm⁻¹, which has a much lower B′ rotational constant than nearby levels of the state, possibly represents the onset of vibronic perturbations by the electronic state; this state is so far unknown, but is predicted by the ab initio calculations of Ahmed et al. [36].     

Growth and vibrational properties of ultra-thin Cr2O3 films grown on Cr(110) studied by RAIRS

Ultra-thin films of Cr₂O₃(0 0 0 1) grown on Cr(1 1 0) were investigated by reflection absorption infrared spectroscopy (RAIRS). An absorption band at 720 cm⁻¹ is assigned to a longitudinal optical phonon of Cr₂O₃. With increasing O₂ exposure, this absorption band shifts to higher frequency, which is qualitatively explained by a simple spring model. After successive oxidation with ¹⁸O₂ and ¹⁶O₂, two absorption bands corresponding to and were distinctly observed suggesting that oxygen diffusion hardly occurs during the oxide growth. Temperature dependence of the RAIRS spectrum taken from the Cr₂O₃ film revealed that the absorption band position shifts to lower frequency along with broadening of the band width. Anharmonic coupling with low-frequency phonons and effects of the antiferromagnetic to paramagnetic phase transition are discussed.     

Millimeter- and submillimeter-wave spectra of AuCl and AuBr in the XΣ electronic ground states

The millimeter- and submillimeter-wave spectra of AuCl and AuBr in the X¹Σ⁺ states were observed by employing a source-modulated microwave spectrometer. The AuCl and AuBr molecules were, respectively, generated in a free space cell by a d.c. glow discharge in Cl₂ and Br₂ with Ar. The gold atoms were supplied by the sputtering reaction from a gold sheet placed on the inner surface of a stainless-steel cathode. Rotational transitions of , , , and in highly excited vibrational states as well as in the ground vibrational states were measured in the region between 189 and 314 GHz. The transition frequencies were analyzed by a least-squares method using a combined-isotopomer Dunham-type term energy expression. The potential constants of gold halides obtained were compared with those of copper and silver halides.     

The 313 nm band system of SeO2. Part 1: vibrational structure

A part of the 313 nm band system of SeO₂ near its origin has been recorded in the gas phase by laser-excitation spectroscopy. The spectrum was recorded with a sample containing the various isotopes of selenium in their natural abundance. The vapour was formed by heating the solid to 320 °C and then cooled in a free-jet expansion. The spectrum obtained is consequently much better resolved than any recorded previously. The vibrational assignments made by King and McLean [J. Mol. Spectrosc. 51 (1974) 363] have been largely confirmed. Some corrections, notably of the v₀⁰ band, and some extensions of the vibrational assignments have allowed the determination of the vibrational parameters for the symmetric stretching (ν₁) and bending (ν₂) vibrations for both the upper and lower electronic states. The first vibrational intervals obtained are as follows:

     

Reassignment of the C-Cl stretching frequency in the Ã(A″) state of CBrCl

In a recent theoretical paper, vibrational frequencies were reported for CBrCl in the and à states. These values agree well with our previously published experimental frequencies, except in the case of , where the theoretical value of 968.3 cm⁻¹ is significantly higher than the experimental value of 712.6 cm⁻¹. This discrepancy prompted a re-examination of the assignments for transitions involving ν₁ in the laser induced fluorescence spectrum. If the progression ν₁ + nν₂ has the assignment of n reduced by 1 (the origin is not observed), a new experimental value of results. The close accord with the theoretical value lends weight to this re-assignment. Consequently we propose that the experimental frequency be changed to .     

Rotational spectrum of HCBr produced by 193-nm laser photolysis of bromoform

The pure rotational spectrum of bromomethylene (HCBr) was studied by kinetic microwave spectroscopy between 420 and 472 GHz. The HCBr radical was produced by 193-nm ArF laser photolysis of bromoform (CHBr₃). More than 130 rotational transitions for both and species in the ground vibrational state were measured involving 1?J?33 and 0?K_a?5. The spectra were well described by an S-reduced Watson Hamiltonian in the I^r representation including the nuclear quadrupole and spin-rotation hyperfine terms. Rotational, centrifugal distortion, nuclear quadrupole and spin-rotation coupling constants were derived for both and species in the ground vibrational state.     

The program complex for computation of spectroscopic characteristics of atomic and molecular gases in UV, visible and IR spectral ranges for a wide range of temperatures and pressures

The program complex intended for calculations, on the personal computer, of spectroscopic properties of separate gases and their mixes in UV, visible and IR ranges is submitted in this work. It consists of algorithms describing spectroscopic characteristics of the neutral and ionized atoms and molecules; banks of initial data, physical, thermodynamic and spectroscopic constants, parameters and package of applied programs.The complex allows the computation of parameters of fine and hyperfine structure in electronic-vibrational-rotational spectrums of diatomic molecules, such as wave numbers, Hönl-London factors, intensities and half-widths of rotational lines; absorption coefficients, absorption cross-sections and emissivity of the heated-up gases with the account of Λ-doubling in ranges of temperatures 200-, pressure 10⁻⁵- and wavelengths 0.1- at anyone spectral intervals of averaging.     

Rotational and vibrational structure in the 288 nm band system of the FeCl2 radical

The laser excitation spectrum of the 288 nm band system of FeCl₂, formed in a free-jet expansion, has been recorded at a rotational temperature of approximately 10 K. Vibronic transitions are observed from the ground state to two close-lying excited electronic states that differ in inversion (g, u) parity. Two extensive progressions in the symmetric stretching vibration have been identified, referred to as Progressions A and B. The main features of Progression A, which is based on the band, are allowed transitions to the excited electronic state of ungerade symmetry. Progression B is built on the band and consists of vibronically induced transitions to the gerade excited state. A substantial decrease in the symmetric stretching vibrational wavenumber is observed on excitation . Local perturbations are found to cause relative shifts between the different isotopomers. Several vibronic bands have been recorded and analysed at rotational resolution for the three isotopomers Fe³⁵Cl₂, Fe³⁵Cl³⁷Cl, and Fe³⁷Cl₂ in natural abundance. All bands show perpendicular rotational structure of a linear molecule, and have been unambiguously assigned to a Ω = 5-4 transition, consistent with the inverted ⁵Δ_g ground state predicted by ab initio and DFT calculations. The zero-point averaged FeCl bond length is determined to be in the upper and lower electronic states. The results show that the molecule is linear in both states.     

Rotational and vibrational temperatures measured in a chemiluminescent flame from FTIR Bi2 emission spectra

Rotational and vibrational temperatures of the Bi₂ dimer have been measured in a chemiluminescent flame. Emission spectra of the Bi₂ a³Σ_u⁺(a₁1_u)→X¹Σ_g⁺(X0_g⁺) transition in the near-infrared region were recorded with a FTIR spectrometer. High-resolution spectra of the 0-3, 0-8, 0-9, 2-3, 4-1, 6-0, 6-1, and 7-1 bands served for the determination of the rotational temperature. It was observed that both rotational and vibrational levels are described well by Boltzmann distributions. The average rotational temperature was found to be consistent with the vibrational temperature . The study has shown that such a very heavy molecule as Bi₂ can serve for temperature measurements by optical emission as reported so far only for light molecules.     

Theory of antiferromagnetic exchange interaction for mixed-valent FeFe spin cluster in model complex of semimethemerythrin

The antiferromagnetic phenomena of both mixed valent Fe^IIIFe^II spin clusters and homodinuclear Fe^IIIFe^III clusters in complexes have been studied by means of our covalent magnetic exchange theoretical method. The sensitive relations between the exchange parameter J and the covalent factors N_A (for Fe^III) and N_B (for Fe^II) and the Fe?Fe separation R have been derived by use of our double-Slater function calculation procedure, the corresponding theoretical curve of J vs. N_A,N_B and R has been obtained. By taking the typical covalent factors of Fe^III and Fe^II, and using the observed Fe-O bond lengths: for Fe^III-O-Fe^II cluster in model complex {[Fe(acacen)]₂ONa}₂; for Fe^III-O-Fe^III cluster in oxyhemerythrin, we obtained the theoretical values: for Fe^III-O-Fe^II cluster and for Fe^III-O-Fe^III cluster. These are in good agreement with the corresponding experimental findings in {[Fe(acacen)]₂ONa}₂ and in oxyhemerythrin, respectively.     

Giant optical anisotropy in R-plane GaN/AlGaN quantum wells caused by valence band mixing effect

This study investigates the optical anisotropy spectrum in the R-plane (i.e., the -oriented layer plane) of GaN/Al_0.2Ga_0.8N quantum wells of different widths. The optical matrix elements in the wurtzite quantum wells are calculated using the k⋅p finite difference scheme. The calculations show that the valence band mixing effect produces giant in-plane optical anisotropy in -oriented GaN/Al_0.2Ga_0.8N quantum wells with a narrow width. The nature of the in-plane optical anisotropy is found to be dependent on the well width. Specifically, it is found that the anisotropy changes from x^′-polarization to y^′-polarization as the well width increases.     

Spectroscopic characterization of the potential energy functions of Ne2 Rydberg states in the vicinity of the Ne(S0) + Ne(4p′) dissociation limits

The gerade autoionizing Rydberg states of Ne₂ have been studied in the range 162 000-172 000 cm⁻¹ by 1 + 1′ resonant two-photon excitation from the Ne₂ X ground state via different vibrational levels of the Ne₂ C state. A rotationally resolved part of the spectrum allowed the determination of the potential energy functions of two states of 1_g and characters in the vicinity of the Ne(2p⁶¹S₀) + Ne (2p⁵4p′) dissociation limit. The presence of maxima in these potential energy functions is interpreted as originating from a repulsive interaction between the Rydberg electron and the neutral atom.