Second order Stark shift of zero-field transitions in protonated and deuterated p-benzoquinones

The second order Stark effect on the zero-field transitions of the lowest triplet state of p-benzoquinone (-h₄ and -d₄) in a host of p-dibromobenzene have been measured and compared. The electric field shifts of the microwave transitions of the perdeuterated compound are 1.9 ± 0.3 times larger than for the protonated molecule. This result indicates that the principal mechanism of the Stark effects is the mixing of the closeby inversion doublet components and not the mixing with a higher electronic state as assumed in previous work.     

ΔF = 2–6 transitions in the hyperfine spectrum of λ = 601.8 nm line of 151Eu

The magnetic field effect of the a ⁸ S _1/2-z ⁸ P _9/2, F = 7 transition lines of ¹⁵¹Eu in magnetic fields up to 400 Gauss has been studied by using laser-atomic-beam-spectroscopy. δF = 2–6 transitions were observed. Results show that the transitions originate from the mixing of the Zeeman states induced by the magnetic field. The condition favourable to observation of the |δF| ≥ 2 transitions especially the transitions with high |δF| values discussed     

Multiphoton ionization spectra of two caged amines

The multiphoton ionization spectra of quinuclidine (ABCO) and triethylenediamine (DABCO) have been measured. All of the observed resonances are two-proton transitions to low-lying localized Rydberg states. For ABCO the lowest energy transitions are assigned as ¹A₁ (3s) ← ¹A₁ (n) 4.84 eV, and ¹E (3p_xy) ← ¹A₁ (n), 5.42 eV. In the case of DABCO, orbitals localized on the nitrogens interact and are split into two new orbitals. In terms of the split orbitals the low energy resonances in DABCO are assigned as ¹E′[3p_xy(?)] ← ¹A₁ (n+_, 4.44 eV, and ¹E″ [3p_xy(+)] ← ¹A₁ (n+), 4.94 eV.     

Lifetime measurements of highly excited Rydberg states of strontium I

Lifetimes of Rydberg states of the triplet-series 5s ns ³ S ₁ withn = 19–23, 35 and 5s nd ³ D ₃ withn = 18–20, 23–28 in the spectrum of neutral strontium have been determined. Observation of the exponential decay after excitation by a pulsed laser in a fast atomic beam and subsequent state-selective field ionization was employed. The lifetimes of the states of the³ S ₁-series show the expectedn*³ dependence on the effective principal quantum number, while the³ D ₃-series is disturbed by configuration mixing. Furthermore, state re-populations induced by black-body radiation have been observed.     

Microwave spectrum of 3-nitrothiophene

The microwave spectrum of 3-nitrothiophene has been studied in the frequency region 26.5–40.0 GHz. The rotational transitions of the ground state and the first six torsionally excited states have been assigned. The ground state rotational constants have been determined to be A_o=4622.61 ± 0.07 MHz, B_o = 1231.751 ± 0.001 MHz and C_o = 973.062 ± 0.001 MHz. The planarity of the molecule has been demonstrated. The first torsional frequency and the barrier to internal rotation of the nitro group have been estimated as 60 cm^?1 and 3.8 kcal/mole, respectively.     

The electronic spectra of 10, 10-dimethylanthracen-9-one crystals: Spin—orbit/vibronic coupling in 3nπ3 states

10, 10-dimethylanthracen-9-one single crystal emission and absorption spectra have been recorded at low temperatures, as well as Raman spectra on the melt. The absorption spectra of both the lowest triplet and lowest excited singlet states clearly show the absorption origins of the three different molecular sites in the triclinic unit cell of the crystal. The emission spectra indicate that substantial spin—orbit/vibronic state mixing occurs, giving rise to transitions between the z sub-level of the lowest ³nπ³ state (T₁) and both totally and non-totally symmetric vibrations of the ground state. The preferred intensity stealing route is from T₁ (z) to S₂(¹ππ³) by spin—orbit coupling with vibronic mixing of S₃ and S₄(¹ππ³, ¹B₂).     

Calorimetric investigations of the MBr−NdBr3 melts (M=Li,Na, K,Cs)

Present work is a part of thermodynamic research program on the MX?LnX₃ system (M=alkali metal,X=Cl, Br andLn=lanthanide). Molar enthalpies of mixing in the LiBr?NdBr₃, NaBr?NdBr₃ and KBr?NdBr₃ liquid binary systems have been determined at temperature 1063 K by direct calorimetry in the whole range of composition. Investigated systems are generally characterized by negative enthalpies of mixing with minimum atX _NdBr3≈0.3–0.4. These enthalpies decrease with decrease of ionic radii of alkali metals. Molar enthalpies of solid-solid and solid-liquid phase transitions of K₃NdBr₆ and Cs₃NdBr₆ have been also determined by differential scanning calorimetry (DSC). K₃NdBr₆ is formed at 689 K from KBr and K₂NdBr₅ with enthalpy of 44.0 kJ·mol^?1 whereas Cs₃NdBr₆ is stable at ambient temperature and undergoes phase transition in the solid state at 731 K with enthalpy of 8.8 kJ·mol^?1. Enthalpies of melting have been also determined.     

Configuration interaction in the 6s n d 1 D 2 and 6s n s 1 S 0 states of Yb probed by lifetime measurements

Radiative lifetimes in the even parity 6s n d ¹ D ₂ (n=6?13) and 6s n s ¹ S ₀ (n=8?14) level series of neutral Yb have been measured. In contrast to a monotonicn*³ behaviour which is expected in the absence of configuration interaction a drastic decrease of the lifetime data was observed in the vicinity of multiply excited states. In addition, for certain levels a strong increase of the lifetime values has been found which may be ascribed to destructive interference due to configuration mixing which can also affect the branching ratios of the radiative decay of these levels.     

Microwave spectrum of propionyl chloride

The microwave spectrum of propionyl chloride has been investigated in the region 18.0–40.0 GHz, and transitions due to a cis conformer have been assigned. This form has a heavy atom planar configuration and the methyl group and the carbonyl oxygen atom are cis to each other. Using the substitution structures of propionic acid and acetyl chloride as molecular models for the propionyl chloride molecule, good agreement is found between observed and calculateò effective rotational constants. For the ³⁵Cl species satellite spectra assigned to the first four excited states of the C-C torsional mode have been observed together with the first excited state of the methyl torsional mode. The ground state spectrum has also been assigned for the ³⁷Cl species. Relative intensity measurements yielded the lowest C-C torsional vibration frequency of 86 ± 10 cm^?1. The CH₃ internal rotation frequency was found to be 197 cm^?1. Nuclear quadrupole coupling constants were determined for the ground state of the ³⁵Cl and ³⁷Cl species. From observed A-E splittings of ^bQ-branch transitions of the first excited state of the methyl torsional mode a barrier to internal rotation was estimated to be V₃ = 2480 ± 40 cal mol^?1 (867 ± 14 cm^?1).     

State selected and oriented molecules: rotationally-resolved photoelectron spectroscopy and dichroism in ionization of symmetric tops

This paper developes a theoretical framework for one-photon, electric dipole ionization of molecules, prepared in a single |JKM〉 rotational state of their ground electronic motion using a hexapole electrostatic field followed by a weak and homogeneous orienting electric field E, by taking also the |J′K′M′〉 eigenstate of the residual photoion into account. This theory has been used to study photoionization in a generic C_3v molecule by the linearly as well as circularly polarized light. Integrated and differential photocurrents plus circular dichroism, obtained from a model calculation, for ionization in two different experimental configurations in 13a ₁ ² orbital of a state selected and oriented CH₃I are discussed. These results show, among other things, that somewhat different propensity rules for |JKM〉 → |J′K′M′〉 transitions are obeyed in different experimental geometries. Also, dichroic effect exists in the photoelectron angular distribution when circularly polarized light is incident perpendicular to E.     

Measurements of the oscillator strengths for the 6p7s (1/2,1/2)1 → 6pnp (1/2,3/2)2 Rydberg transitions of lead

We report experimentally determined oscillator strength distribution in the bound region of lead corresponding to the 6p7s (1/2, 1/2)₁ → 6pnp (1/2, 3/2)₂ (20 ≤ n ≤ 52) Rydberg transitions. The absolute value of the photoionization cross section from the 6p7s (1/2, 1/2)₁ excited state at the first ionization threshold 6p (²P_1/2) has been determined as 27 ± 4 Mb using the saturation absorption technique. The threshold value of the photoionization cross section is used to calibrate the oscillator strengths of the above mentioned Rydberg transitions. Moreover, oscillator strengths in the bound region smoothly connect with the differential oscillator strength density at the first ionization threshold, and verify the fundamental condition of quantum defect theory.     

A precise determination of the first ionization potential of benzene

The first ionization potentials of benzene and benzene-d₆ have been precisely determined by the extrapolation of three-photon resonant Rydberg states in the four-photon ionization spectrum of the jet-cooled molecule. The convergence of resolved transitions in two Rydberg series for principal quantum numbers as high as 14 (-h₆) and 15 (-d₆) establish adiabatic thtesholds of 74573.0 ± 2.0 cm^?1, and 74592.5 = ± 1.2 cm^?1, respectively. These results are crucial for the understanding of the many excited states of benzene in terms of quantum defect theory. Precise quantum defects have been obtained for several Rydberg series and their variation with principal quantum number is reported. The results strongly suggest that the R? series of Wilkinson is derived from aπ(e_1g)→ nf±1 Rydberg excitation.     

Ionization of water in interfacial electric fields: An electrochemical view

High electric fields promote ionization of water, yet relatively little is known about this topic due to the difficulty of generating such fields. The high field capability of field emitter tips enables study of ionization in water layers. Results from this work include ionization fields, water layer morphology, dielectric properties, coadsorbate interactions, cluster distributions of hydrated hydronium ions H⁺(H₂O)_m, and field ionization images. These experimental results, combined with theoretical findings, are interpreted in the context of four examples from electrochemistry; double layer structure, hydrogen oxidation, CO oxidation, and oxygen reduction; to reveal the research frontier in interfacial ionization of water.     

Microwave spectrum,dipole moment and barrier to internal rotation of trans-methyl glyoxal

The microwave spectrum of the trans conformer of methyl glyoxal has been investigated in the frequency range from 8 to 40 GHz. The rotational constants have been determined for the A state: A = 9102.4332(31), B = 4439.8832(27) and C = 3038.9404(22) MHz. Quantitative measurements of the Stark effect have yielded the components of the electric dipole moment: μ_a = 0.1597(11), μ_b = 0.9620(7) and μ_total = 0.9751(7) D. From the splittings of rotational transitions the three-fold barrier to internal rotation of the methyl top has been found to be V₃ = 269.1 (3) cm^?1.     

Spectre hertzien du fluorure de thionyle: Détermination des coefficients de distorsion centrifuge

The microwave spectrum of thionyl fluoride has been investigated in the spectral region 40–70 GHz. The assignment of many high J transitions gives all rotational constants and quartic and sextic Watson's parameters for the ground state and the excited vibrational state v₄.     

Spectra and structure of organophosphorus compounds: XVII. Infrared and Raman spectra. vibrational assignment and barriers to internal rotation for t-butylphosphine

The infrared spectra of gaseous and solid tertiary-butylphosphine, [(CH₃)₃CPH₂], have been recorded from 50 cm^?1 to 3500 cm^?1. The Raman spectra of gaseous, liquid and solid (CH₃)₃CPH₂ have been recorded from 10 to 3500 cm^?1. A vibrational assignment of the 42 normal modes has been made. A harmonic approximation of the methyl torsional barrier from observed transitions in the solid state gave a result of 4.22 kcal mol^?1 and 3.81 kcal mol^?1 in the gaseous state. Hot band transitions for the phosphino torsional mode have been observed. The potential function for internal rotation about the C-P bond has been calculated. The two potential constants were determined to be: V₃ = 2.79 ± 0.01 kcal mol^?1 and V₆ = 0.07 ± 0.01 kcal mol^?1.     

All-valence-electron Cl calculations on the electronic spectrum of diborane

All-valence-electron Cl calculations have been carried out for diborane B₂H₆ and its positive ion employing a rather large double-zeta AO basis including polarization functions in order to study the electronic spectrum of this system. Transitions from four different valence MOs are found to lead to low-lying electronic transitions of both Rydberg and valence type in each case. Ad mixture of valence character in the otherwise Rydberg-like (nx, 3s), (ny, 3s) and (σ, 3pz) transitions calculated to lie between 11.0 and 11.6 eV is indicated as being primarily responsible for the highly intense shoulder found in this region of the B₂H₆ spectrum. The other strong feature with essentially continuous absorption peaking at 9.3 eV is suggested to result from superposition of several Rydberg-type transitions in the generally broad absorption pattern expected for the ¹(π,π^*) species at significantly higher vertical excitation energy. Quite good agreement is obtained between calculation and experiment for all of the six lowest IPs of diborane and also for the locations of the ¹(n, π^*) and ¹(σ, π^*) transitions previously assigned to the two weak features observed at 6.8 and 8.3 eV in this spectrum.     

Electronically excited and ionized states of the chlorine molecule

Potentials curves for the ground and excited states of the chlorine molecules and its positive and negative ions have been calculated by means of the MRD-CI method. The standard AO basis employed consists of 74 functions including two atomic d and one set of s and p bond species, and the results at the corresponding full CI level are estimated for each state via a perturbation correction. Special emphasis is placed upon the treatment of Rydberg-valence mixing in this system, which phenomenon is found to be essential to the understanding of Cl₂ electronic absorption spectrum. All singlet states which correlate with the lowest dissociation limit plus many others which go to ionic Cl⁺+Cl^? or Rydberg Cl+Cl asymptotes are given explicit consideration. Among the triplet species of Cl₂ which dissociate into the ground state atoms only the ³Π_u state is not repulsive. The calculated D₀ value for the ground state is 2.455 eV compared to the experimental value of 2.475 eV, while the vertical ionization energy and electron affinity are found to be 11.48 and 2.38 eV respectively, also in very good agreement with the corresponding measured data of 11.50 and 2.51 ± 0.1 eV. In addition to Cl₂ laser line is confirmed to result from a ³Π_g → ³Π_u emission, whereby the calculated downward vertical transition energy of 4.86 eV fits in quite well with the known location of this line at 4.805 eV. The first two dipole-allowed transitions from the ground state of chlorine involve ¹Σ_u⁺ and ¹Π_u states which are calculated to be nearly isoenergetic, and these results also match very well with the location of the first absorption band in this spectrum. Finally quite similarly as in O₂ it is found that an avoided crossing between Rydberg and valences states produces a relatively steep potential well for an upper state (2 ¹Σ_u⁺), whose location concides with that of a second absorption band recently observed in synchrotron radiation studies.     

Microwave—optical double resonance in the A1A2 excited state of thioformaldehyde

Microwave—optical double resonance experiments have been carried out on the 4_o¹ band of the $\text{A}$¹A₂$\text{X}$¹A₁ system of thioformaldehyde (H₂CS). More than 100 microwave and radiofrequency transitions have been observed in the $\text{A}$¹A₂ excited state. Many of these transitions are magnetically sensitive. Some of the excited state levels are perturbed by triplet levels and others by high vibrational levels of the ground state.     

Excited State Dynamics of Isocyano Rhenium(I) Phenanthroline Complexes from Time-Resolved Spectroscopy

The photophysical processes in a series of isocyano Re(I) phenanthroline complexes {[Re(CNR)_n(CO)_4-n(phen)](PF₆); n=2, 3, 4, R=2,6-(ⁱPr)₂C₆H₃- or ^tBu- (n=2)} in acetonitrile have been studied by resonance Raman spectroscopy, transient resonance Raman spectroscopy, and femtosecond / nanosecond transient spectroscopy to elucidate the nature of their electronic transitions and emissive excited state(s). The kinetics of the intersystem crossing, vibrational relaxation and radiative decay of the metal-to-ligand charge transfer {MLCT [dπ(Re)→π*(phen)]} excited state have also been determined.