Absorption and emission spectra of the lowest triplet state in hexachloroacetone

T₁ ← S₀ absorption and T₁ → S₀ phosphorescence spectra of neat cystalline hexachloroacetone have been analyzed at 4.2°K. From the lifetime and energy the upper state is assigned as ³nπ^*. The spectra are sharp compared to other aliphatic ketones, with the 0-0 band at 26 248 ± 2 cm ^?1. The phosphorescence shows two strong progressions; one involving the CO stretching mode at 1784 cm^?1 (x), the other a long progression of at least 8 bands involving a mode at 143 cm^t-1 (a). The 143 cm^?1 progression forming mode can best be asigned to the CO out-of-plane wagging vibration. The absorption shows the same two strong progressions, reduced in frequency to 1270 cm^t-1 and 123 cm^?1, respectively, but with the progression in mode a broadened with increasing n. The broadening is interpreted as arising from inversion doublets; the close harmonicity up to n = 5 allowing the potential barrier to inversion to be estimated as > 700 cm^?1. A feature of the spectra is the absence of low frequency torsional modes suggesting lack of pseudo Jahn-Teller distortion of the triplet state potential surface. For comparison, the phosphorescence of crystalline hexafluoroacetone was also studied at 4.2°K. The spectrum exhibits broad bandedness with a 00 band tentatively assigned at 26 870 ± 20 cm^?1.     

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).     

Investigation of excited‐state properties of fluorene–thiophene oligomers by the SAC‐CI theoretical approach

Excited states of fluorene‐ethylenedioxythiophene (FEDOT) and fluorene‐S,S‐dioxide‐thiophene (FTSO2) monomers and dimers were studied by the symmetry‐adapted cluster (SAC)‐configuration interaction (CI) method. The absorption and emission peaks observed in the experimental spectra were theoretically assigned. The first three excited states of the optimized conformers, and the conformers of several torsional angles, were computed by SAC‐CI/D95(d). Accurate absorption spectra were simulated by taking the thermal average for the conformers of torsional angles from 0° to 90°. The conformers of torsional angles 0°, 15°, and 30° mainly contributed to the absorption spectra. The full width at half‐maximum of the FEDOT absorption band is 0.60 eV (4839 cm^?1), which agrees very well with the experimental value of 0.61 eV (4900 cm^?1). The maximum absorption wavelength is located at 303 nm, which is close to those of the experimental band (327 nm). The calculated absorption spectrum of FTSO2 showed two bands in the range of 225–450 nm. This agrees very well with the available experimental spectrum of a polymer of FTSO2, where two bands are detected. The excited‐state geometries were investigated by CIS/6‐31G(d). These showed a quinoid‐type structure which exhibited a shortening of the inter‐ring distance (0.06 Å for FEDOT and 0.04 Å for FTSO2). The calculated emission energy of FEDOT is 3.43 eV, which agrees very well with the available experimental data (3.46 eV). The fwhm_E is about 0.49 eV (3952 cm^?1), while the experimental fwhm is 0.43 eV (3500 cm^?1). For FTSO2, two bands were also found in the emission spectrum. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Long-Range LMCT Coupling in EuIII Coordination Polymers for an Effective Molecular Luminescent Thermometer**

A design for an effective molecular luminescent thermometer based on long-range electronic coupling in lanthanide coordination polymers is proposed. The coordination polymers are composed of lanthanide ions Eu^III and Gd^III, three anionic ligands (hexafluoroacetylacetonate), and a chrysene-based phosphine oxide bridges (6,12-bis(diphenylphosphoryl)chrysene). The zig-zag orientation of the single polymer chains induces the formation of packed coordination structures containing multiple sites for CH-F intermolecular interactions, resulting in thermal stability above 350 °C. The electronic coupling is controlled by changing the concentration of the Gd^III ion in the Eu^III-Gd^III polymer. The emission quantum yield and the maximum relative temperature sensitivity (S_m) of emission lifetimes for the Eu^III-Gd^III polymer (Eu:Gd=1:1, Φ_tot=52 %, S_m=3.73 % K⁻¹) were higher than those for the pure Eu^III coordination polymer (Φ_tot=36 %, S_m=2.70 % K⁻¹), respectively. Enhanced temperature sensing properties are caused by control of long-range electronic coupling based on phosphine oxide with chrysene framework.     

Molecular structure and conformation of gaseous chloroacetyl chloride as determined by electron diffraction

Chloroacetyl chloride is studied by gas-phase electron diffraction at nozzle-tip tempera- tures of 18, 110 and 215°C. The molecules exist as a mixture of anti and gauche confor- mers with the anti form the more stable. The composition (mole fraction) of the vapor with uncertainties estimated at 2σ is found to be 0.770 (0.070), 0.673 (0.086) and 0.572 (0.086) at 18, 110 and 215°C, respectively. These values correspond to an energy difference with estimated standard deviation ΔE^o = E^o_g -E^o_a = 1.3 ± 0.4 kcal mol^?1 and an entropy difference ΔS^o = S^o_g -S^o_a = 0.7 ± 1.1 cal mol^?1 K^?1. Certain of the diffraction results permit the evaluation of an approximate torsional potential function of the form 2V = V₁(1 - cos φ) + V₂(1 - cos 2φ) + V₃(1 - cos 3φ); the results are V₁ = 1.19 ± 0.33, V₂ = 0.56 ± 0.20 and V₃ = 0.94 ± 0.12, all in kcal mol^?1. The results for the distance (r_a), angle (_∠α) and r.m.s. amplitude parameters obtained at the three temperatures are entirely consistent. At 18°C the more important parameters are, with estimated uncertainties of 2σ, r(C-H) = 1.062(0.030) Å, r(CO) = 1.182(0.004) Å, r(C-C) = 1.521(0.009) Å. r(CO-Cl) = 1.772(0.016) Å, r(CH₂-Cl) = 1.782(0.018) Å, ∠C-C-0 = 126.9(0.9)°, ∠CH₂-CO-C1 = 110.0(0.7)°,∠CO-CH₂-C1 = 112.9(1–7)°, ∠H-C-H = 109.5° (assumed), ∠φ (gauche torsion angle relative to 0° for the anti form) = 116.4(7.7)°, δ (r.m.s. amplitude of torsional vibration in the anti conformer) == 17.5(4.2)°.     

Highly resolved structure of the electronic spectra of azulene in frozen hydrocarbon matrices

Vibronic structures of electronic spectra of azulene embedded into various hydrocarbon matrices are examined at 77°K. High-resolution spectra are obtained using crystalline matrices of isooctane and methylcyclohexane. The O-O bands of third and fourth electronic transitions (33836 and 35550 cm^?1, respectively, in the low-temperature modification of the isooctane matrix) are identified in the absorption spectrum of azulene. Using the P-P-P approximation with the unified parametrization the lowest excited states energies as well as bond lengths for the S_o and their respective changes in the S₁ and S₂ electronic states are calculated. Differences in the vibrational frequencies found for the respective electronic states of the azulene molecule are discussed in connection with the lack of the mirror symmetry between the S₂←S_o absorption and S₂→S_o fluorescence.     

The structure and dynamics of the copper(II)—l-proline 1:2 complex in solution

The ¹³C relaxation times (T₁ and T₂) and isotropic contact shifts (Δω) of a one molar aqueous solution of l-proline at pH = 11 (or pD = 11.4) containing ca 10^?4 M copper(II) perchlorate are measured at 62.86 MHz over a temperature range of 26–70°C. The purely dipolar longitudinal relaxation of carbon-13 nuclei contrasting with purely scalar transverse relaxation allowed us to extract carbon-to-metal distances (through T₁ measurements) and hyperfine coupling constants and dynamic parameters (from T₂ and Δω measurements). The structure of the complex in solution is found closely similar to that in the solid state. Curve-fitting procedures allowed us to derive the hyperfine electron—carbon coupling constants A_c = ?1.95, + 0.42, + 1.90 and ?1.70 MHz for carbons α, β, γ, δ, of the pyrrolidinic ring, the reorientation correlation time of the complex, τ_R (25°C) = 1.15 × 10^?10 sec, the l-proline exchange rate, k_M (25°C) = 4.0 × 10⁵ sec^?1 (and the corresponding activation parameters ΔH^≠ = 9.0 kcal mol^?1 and ΔS^≠ = ?0.7 e.u.), and the electronic relaxation time, T_1e = 1.13 × 10^?8 sec (at 25°C). The latter value was found in agreement with the one computed from ESR data and the above τ_R value, showing the predominant contributions of spin—rotation interaction and, to a lesser extent, of the effect of g-tensor anisotropy to the electronic relaxation rate.     

Molecular structure and conformation of 2,3-dichloro-1-propene as determined by gas-phase electron diffraction

The molecular structure and conformation of 2,3-dichloro-1-propene have been determined by gas-phase electron diffraction at nozzle temperatures of 24, 90 and 273°C. The molecules exist as a mixture of two conformers with the chlorine atoms anti (torsion angle ∠φ = 0°) or gauche (∠φ = 109°) to each other and with the anti form the more stable. The composition (mole fraction) of the vapor with uncertainties estimated at 2σ was found to be 0.55 (0.08), 0.49 (0.08) and 0.41 (0.10) at 24, 90 and 273°, respectively. These values correspond to an energy difference with estimated standard deviation ΔE° = E°_g-E°_a = 0.7 ± 0.3 kcal mol^?1 and an entropy difference ΔS° = S°_g-S°_a = 0.6 ± 0.9 cal mol^?1 K^?1. Some of the diffraction results, together with spectroscopic observations, permit the evaluation of an approximate torsional potential function of the form 2V = V₁ (1 - cos φ) + V₂ (1 - cos 2φ) + V₃ (1 - cos 3φ); the results are V₁ = 4.4 ± 0.5, V₂ = ?2.9 ± 0.5 and V₃ = 4.8 ± 0.2, all in kcal mol^?1. The results at 24°C for the distance (r_a) and angle (∠_α) parameters, with estimated uncertainties of 2σ, are: r(C_sp²-H) = 1.098(0.020)Å, r(C_sp³-H) = 1.103(0.020)Å, r(CC) = 1.334(0.009)Å, r(C-C) = 1.504(0.013)Å, r(C_sp²-Cl) = 1.752(0.021)Å, r(C_sp³-Cl) = 1.776(0.020)Å, ∠C-CC = 127.6(1.1)°, ∠C_sp³-C_sp²-Cl = 110.2(1.0), ∠C_sp²-C_sp³-Cl = 113.1(1.2)°, ∠H-C_sp³-H = 109.5° (assumed), ∠CC-H = 120.0° (assumed) and ∠φ = 108.9(3.4)°.     

Torsional symmetry dependence of S1 dynamics in molecules that undergo methyl internal rotation

The single‐rovibronic‐level fluorescence of “intermediate‐case” molecules that undergo methyl internal rotation is strongly influenced by the torsional symmetry of the lowest excited singlet state (S₁). The most dramatic example of such symmetry dependence comes from our recent finding that the intensities of the e–e transitions in the high‐resolution S₁←S₀ fluorescence excitation spectra of jet‐cooled acetaldehyde become very weak relative to the a–a transitions at higher beam temperatures. In this study, we rationalize this remarkable torsional symmetry dependence of electronic relaxation in acetaldehyde on the basis of internal‐overall rotation coupling that leads to symmetry‐selective increase in the density of states for singlet‐triplet coupling. Related observations by others on aliphatic carbonyls and diazabenzenes are also discussed within the context of the coupling between the internal and overall rotation. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 167–176, 1999     

The crystal structure of niobium trisulfide,NbS3

The crystal structure of NbS₃ was determined from single-crystal diffractometer data obtained with MoKα radiation. The compound is triclinic, space group $\text{P}\text{1}$, with: a 4.963(2) Å; b = 6.730(2) Å; c = 9.144(4)Å; α = 90°; β = 97.17(1)°; γ = 90°. The structure is closely related to the ZrSe₃ structure type; it shows that the compound can be formulated as Nb⁴⁺(S₂)^2?S^2?, in agreement with XPS spectra. The main difference with ZrSe₃ is that the Nb atoms are shifted from the mirror planes of the surrounding bicapped trigonal prisms of sulfur atoms to form NbNb pairs (NbNb = 3.04 Å); this causes a doubling of the b axis relative to ZrSe₃ and a decrease of the symmetry to triclinic.     

Theoretical study on geometry and spectroscopic properties of 1,1′-binaphthyl in the electronic ground and first excited singlet states

Equilibrium geometries for the electronic ground and first excited singlet states of 1,1'-binaphthyl have been calculated by minimization of the total energy with respect to all internal coordinates. Using these results, an interpretation of the fluorescence S₁→ S₀ and absorption spectra S_m ← S₀ and S_n ← S₁ in rigid and fluid solutions is given.For the first time the equilibrium geometry of the first excited singlet state of 1, 1′-binaphthyl has been calculated. On excitation to the S₁ state the dihedral angle θ between the two naphthalene moieties is de- creased from 61 ° to 41 °. A detailed survey of CH bond lengths in the S₀ and S₁ states has been given. This result should be of particular importance for the theoretical treatment of radiationless transitions.Using equilibrium geometries for the S₀ and S₁ states a satisfactory interpretation of the S_m ← S₀ and S_n ← S₁ absorption spectra as well as of the fluorescence spectra in fluid and rigid solutions can be given. Concerning the S_n ← S₁ absorption spectrum in fluid solution, the calculations predict a strong absorption (A ← B transition) in the still uninvestigated region of energies lower than 11000 cm^?1.From the results of this paper and of other calculations it can be concluded that the Warshel-Karplus method yields reliable equilibrium geometries for electronic ground and excited states of unsaturated hydrocarbons [22,23].     

The phenomenon of conglomerate crystallization of organic compounds. Part 4. The structures of 2,2′-biphenyldisulfide (I) and 2,2′-biphenyldisulfide monoxide (II)

A racemic solution of 2,2′-biphenyldisulfide ( I ), C₁₂H₈S₂, produces conglomerate crystals of ( I ) belonging in space group P3₂21 (no. 154) with lattice constants: a = 7.38 (3) Å, b = 7.38 (3), c = 16.20 (2) Å; V = 766.6 ų and d(calc; M.W. = 216.32, z = 3) = 1.406 g-cm⁻³, d(meas) = 1.47 g-cm⁻³. A total of 1150 data were collected over the range of 4° ≤ 2θ ≤ 60° using film data (Weissenberg); of these, 448 [independent and with I ≥ 3σ(I)] were used in the structural analysis. Refinement converged to final residuals of 0.080 and 0.082 for R(F) and R_W(F), respectively. The molecule is located at the twofold axis of the space group. A solution of 2,2′-biphenyldisulfide mono-oxide ( II ), C₁₂H₈S₂O, produces centrosymmetric crystals of II belonging in space group P2₁/c with lattice constants: a = 9.947 (1) Å, b = 7.162 (2), c = 15.420 (3) Å, and β = 107.56 (1)°; V = 107.56 (1) ų and d(calc; M.W. = 232.31, Z = 4) = 1.473 g-cm⁻³. A total of 2114 data were collected over the range of 4° ≤ 2θ ≤ 50°; of these, 1089 [independent and with I ≥ 2.5σ(I)] were used in the structural analysis. Data were corrected for absorption (μ = 4.539 cm⁻¹), and the relative transmission coefficients ranged from 0.9198 to 0.9998. Refinement converged to final residuals of 0.0313 and 0.0300 for R(F) and R_w(F), respectively. For I , the central six-membered ring C₄S₂ contains a helical C₂S₂ fragment whose conformational chirality is defined by a torsional angle of 59.98°. The benzene rings are the expected, planar hexagons characteristic of aryl rings. By comparison with I , the torsional angle of the C₂S₂ fragment of the mono-oxide is diminished (52.9°) by the introduction of the S=O fragment. We believe alteration of molecules (such as functionalization) causing large changes in torsional angles of helical fragments of molecules may play a role in the selection of their crystallization mode; however, it is not the only factor dictating that choice, which is also affected by steric hindrance to the formation of short intermolecular contacts leading, in the solid state, to the formation of homochiral, infinite helical strings, as we shall demonstrate in the text. This study clearly shows the influence of those contacts on the formation of the strings. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:65–74, 1998     

A Raman spectroscopic study of the low-frequency vibrations in anisole and anisole-d3

Low-frequency Raman spectra of solid anisole and of solid anisole-d₃ have been recorded at 130 K. The phenyl torsion observed at 148 cm^?1 is shifted to 133 cm^?1 upon deuteration of the methyl group. The twofold torsional barriers calculated from these frequencies are 4033 ± 110 cm^?1 and 4094 ± 123 cm^?1 indicating that coupling to other low-frequency modes in both cases is of the same order of magnitude. The methyl torsional mode was observed at 285 cm^?1 in the spectrum of solid anisole and at 183 cm^?1 in the spectrum of anisole-d₃. The threefold barriers calculated using these frequencies are 1847 ± 20 cm^?1 and 1465 ± 18 cm^?1 respectively. These barrier values indicate that the methyl torsion is coupled to another low-frequency mode. A doublet centered at 230 cm^?1 in anisole is shifted to 245 cm^?1 in anisole-d₃; it is proposed that this is due to a ring mode coupled to the methyl torsion. The splitting is interpreted as an example of Davydov splitting.     

Fluorescence spectra and intramolecular vibrational redistribution in jet-cooled perylene

The jet-cooled fluorescence spectra of perylene excited to the S₁ state with E_vib = 0–1600 cm^?1 are recorded and analyzed. For E_vib <800 cm^?1 only the resonant fluorescence was detected. Ground- and excited-state frequencies of 14 low-frequency normal modes are determined. A drastic change in frequency of the “butterfly” modes upon electronic excitation shows that perylene slightly deviates from planarity in its ground state and is more rigid in the excited singlet state. For a number of levels in the E_vib = 800–1600 cm^?1 range, the fluorescence is composed of the resonant emission and of non-resonant (“‘relaxed’”) bands. It is shown that apparently single bands in the fluorescence-excitation spectrum correspond to ovelapping bands pumping different molecular eigenstates resulting from the intrastate coupling. The relative role of the anharmonicity and of the Coriolis interaction are discussed. The data are treated in terms of a selective coupling between doorway and hallway states with the coupling constant rapidly decreasing with the difference in the overall vibrational quantum number between initial and final state.     

Microwave spectroscopic study on the molecular structure and the quadrupole coupling constants of thionyl chloride

Microwave spectra of thionyl chloride, SO³⁵Cl₂ and SO³⁵Cl³⁷Cl, in the frequency range 8–25 GHz have been analyzed. The rotational constants have been obtained from the low J transition frequencies. The r_S coordinates of Cl atoms and the r_o structure have been evaluated with some assumptions: r(S-O) = 1.435 ± 0.011± Å, r(S—Cl) = 2.072 0.005 Å, ∠ OSCl = 108.00 ± 0.06°, ∠ ClSCl = 97.15 ± 0.30°. Nuclear quadrupole coupling constants have been obtained for the SO³⁵Cl₂, species: x_aa = ?25.02 ± 0.04 MHz, x(_bb = ?0.25 ± 0.04 MHz, X_cc = 25.27 ± 0.08 MHz, and X_zz = ?96.75 MHz. The values obtained are compared with those of other workers.     

Microwave spectrum,conformation, intramolecular hydrogen bond,dipole moment, 14N quadrupole coupling constants and centrifugal distortion of 2flu

Microwave spectra of CH₂FCONH₂, CH₂FCOND(1)H(2), CH₂FCONH-(1)D(2), and CH₂FCOND₂ are reported. The stable form of the molecule is shown to possess a planar FCCONH₂ skeleton, with two out-of-plane hydrogens. The C-F and CO bonds are trans to one another and a weak intramolecular hydrogen bond is formed between the fluorine atom and the nearest amide group hydrogen atom stabilizing the identified rotamer. Other conformations are not present in concentrations exceeding 10% of the total. Nine vibrationally excited states were assigned. Six of these were attributed to the C-C torsional mode and one to the lowest in-plane bending mode. The first excited state of -NH_z out-of-plane deformation mode was tentatively assigned. Relative intensity measurements yielded 114±14 cm^?1 for C-C torsional mode and 239±20 cm^?1 for the in-plane bending mode. The dipole moment was determined asμ_a = 1.27±0.01 D, μ_b = 1.67±0.02 D, and μ_tot = 2.10±0.02 D, while the ¹⁴N quadrupole coupling constants were found to be χ_aa = 1.6±0.2 MHz, χ_bb = 1.6±0.2 MHz and χ_cc = ?3.2±0.3 MHz.     

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).     

Structures of the silver complexes with lutidines according to the NMR data. Crystal structure of [AgNO3(3,5-Lut)2]

The silver(I) nitrate complexes with 2,3-, 2,4-, 2,6-, and 3,5-lutidine (Lut, dimethylpyridine C₇H₉N), [AgNO₃(Lut)₂], are synthesized and studied by multinuclear NMR (¹H, ¹³C, and ¹⁵N) in various solvents (chloroform, dimethyl sulfoxide, and acetonitrile). The influence of steric and electronic factors of the organic ligand on the parameters of the NMR spectra is revealed. It is shown that the ¹⁵N NMR spectra are the most informative. The structure of complex [AgNO₃(3,5-Lut)₂] is determined. The crystals are monoclinic, space group C2/c, a = 14.599(1) Å, b = 8.422(1) Å, c = 12.954(1) Å, β = 99.60(1)°, V = 1570(2) ų, ρ_calcd = 1.625 g/cm³, Z = 4. The structure is built of discrete neutral complexes [AgNO₃(3,5-Lut)₂]. The coordination mode of the Ag⁺ ion includes two nitrogen atoms of two crystallographically equivalent lutidine ligands (Ag-N 2.194(5) Å, angle NAgN 147.6(3)°). The nitrate ion behaves as a weak chelating ligand with respect to the Ag⁺ ion (Ag…O 2.674(6) Å).     

Microwave spectrum,conformational preference,intramolecular hydrogen bond,barrier to internal rotation,dipole moment,and centrifugal distortion of 1-fluoro-2-propanol

The microwave spectra of 1-fluoro-2-propanol, CH ₃CH(OH)CH ₂F, and one deuterated species, CH₃,CH(OD)CH₂F, have been investigated in the 18–30 GHz spectral region. Only one rotamer with an intramolecular hydrogen bond formed between the fluorine atom and the hydroxyl group was assigned. This conformation is also characterized by having the C-F bond approximately anti to the methyl group. The FCCO dihedral angle is 59 ± 2° and the HOCC dihedral angle is 58 ± 3°. Further conformations, if they exist, are at least 0.75 kcal mol^?1 less stable. Five vibrationally excited states belonging to four different normal modes were assigned and their fundamental frequencies determined. The barrier to internal rotation of the methyl group was found to be 2796 ± 50 cal mol^?1. The dipole moment is μ_a = 0.510 ± 0.009 D, μ_b = 1.496 t 0.026 D, μ_c = 0.298 ± 0.014 D, and μ_tot = 1.608 ± 0.030 D. Extensive centrifugal distortion analyses were carried out for the ground and the first excited state of the heavy-atom torsional mode and accurate values were determined for all quartic and two sextic coefficients.     

Rotational relaxation in S1 glyoxal: Cross sections and a search for propensity rules

Details of rotational energy transfer from a few selected K′J′ levels in the zero point vibrational level of ¹Au(S₁) glyoxal vapor have been studied. The cross section for destruction of an initial K′J′ level by rotational relaxation in collision with ground electronic state glyoxal is about 240 A² or 4.5 times gas kinetic. Much of the rotational transfer within the S₁ state occurs with large ΔK′ and ΔJ′. No strong propensities for △K′ = 0, ± 1, ± 2, or ± 3 with small ΔJ′ changes occur in collisions with ground electronic state glyoxal. The study was made by examination of the rotational structure in the 5₁⁰ emission band at various pressures after excitation in the 0,0 band of the S₁—S₀ system with the 454.5 nm argon ion line.