Vibrational spectra of tetramethyleyclobutane-1-one-3-thione and the fully deuterated derivative

Raman and i.r. spectra of tetramethylcyclobutane-1-one-3-thione (TMCBOT) and the fully deuterated derivative TMCBOT-_d¹² have been recorded. A fairly complete set of vibrational frequencies and assignments are given for the two molecules. The CO stretching mode was observed as a very strong Fermi doublet in the infrared spectrum of TMCBOT at 1811/1782 cm⁻¹. For TMCBOT-d₁₂ a similar doublet was observed at 1808/1775 cm⁻¹. The CS stretching mode was assigned to bands at 1303 cm⁻¹ for TMCBOT and 1307 cm⁻¹ for the deuterated molecule.     

A new molecular electronic emission spectrum observed in the reaction of F2 with CS2

A novel emission spectrum extending from 5500 to 8600 Å has been observed during the gas-phase reaction of F₂ with CS₂. Long progressions in the lower-state (presumably the ground-state) bending frequency and shorter progressions in a ground-state stretching frequency were observed. A partial vibrational analysis is reported, from which two new frequencies are obtained: v″₂ = 356 ± 5 and v″₃ = 8 31 ± 8 cm⁻¹ .The electronic origin lies near 18500 ± 1200 cm⁻¹. The spectrum is tentatively assigned to the FCS radical.     

Spectra and structure of small ring compounds—LX. Raman and infrared spectra,conformational stability,normal coordinate analysis,and ab initio calculations of cyclobutyl acetylene

The Raman spectra (3400 to 10 cm⁻¹ of gaseous, liquid (with qualitative depolarization values) and solid cyclobutyl acetylene, c-C₄H₇CCH, have been recorded. Additionally, the infrared spectra (3500 to 90 cm⁻¹ of the gas and solid have been obtained. The spectra of the fluid phases are consistent with two stable conformers existing at ambient temperature. These data have been interpreted on the basis that the equatorial conformer is more stable than the high energy axial form in both the gas- and liquid-phases, and is the only conformer present in the solid. Two Q-branches are observed in the low frequency vibrational spectra of the gas at 133 and 118 cm⁻¹ and are assigned to the fundamental ring puckering vibration and an associated upper state transition of the low energy equatorial conformer. These data have been used to approximate the form of the potential function governing ring inversion. Experimental values for the enthalpy difference between the two conformers have been determined for both the gas, 282 ± 49 cm⁻¹, and the liquid, 181 ± 15 cm⁻¹, from relative intensities of a pair of Raman lines over 71 and 100°C temperature ranges, respectively. The structure, conformational stability, inversion barrier and vibrational frequencies have been determined by ab initio calculations using the 3-21G and/or 6-31G* basis sets. These calculated results are discussed in comparison to those determined from experiment and to corresponding quantities for some similar molecules.     

Velocity modulation laser spectroscopy of vibrationally excited CF+ determination of the molecular potential function

The lowest six vibrational hot bands of CF⁺ have been measured in a helium/C₂F₆ discharge by velocity modulation laser spectroscopy. A total of 56 transitions has been fitted to Dunham expansion for v = 0–7, yielding the parameters: ω_e = 1792.6654(18) cm⁻¹B_e = 1.7204176(75) cm⁻¹, Y₂₀, = −13.22968(54) cm⁻¹, and D₀ = 62086(30) cm⁻¹. The rotational temperature of CF⁺ in the plasma is near 650 K and the vibrational temperature is approximately 5200 K.     

The X-ray crystal structure of di-η5-cyclopentadienylthiophenolatoamminemolybdenum(IV) hexafluorophosphate solvate [Mo(η5-C5H5)2(NH3)(SC6H5)][PF6] · (CH32CO

Crystals of [Mo(η⁵-C₅H₅)₂(NH₃)(SC₆H₅)][PF₆] · (CH₃)₂CO solvate are monoclinic, space group P2₁/n, a 9.777(1), b 11.6343(2), c 19.656(4) Å, β 93.60(1)°, V 2231-46 ų, Z  D_c 1.617 g cm⁻³, μ(Mo-K_α) 7.21 cm⁻¹. The structure was solved by Patterson and difference Fourier electron density synthesis and refined to R (F)  0.047 and R_w(F)  0.057 for 3293 observed reflections. The molybdenum atom has the usual distorted tetrahedral geometry comprising the two MoCp (Cp  η⁵-C₅H₅) ring normals (MoCp 1.988(13), 1.989(15) Å), one Mo-NH₃ (MoN 2.226(12) Å), and one MoSc₆H₅ (MoS 2.465(5) Å). Extended HMO and steric energy calculations were made in order to account for the geometry adopted by the thiolato ligand in this complex.     

Two-photon sequential absorption spectroscopy of the E(0+) state of iodine monofluoride

The energy levels of a new state of iodine monofluoride lying 5 eV above the ground state have been measured using the two-photon sequential absorption technique. Eleven vibrational levels of the state were measured. A vibrational and rotational analysis gives the spectroscopic constants as T_e = 41291.96 cm⁻¹, ω_e = 248.76 cm⁻¹, ω_eχ_e = 0.4951 cm⁻¹ and B_e = 0.12920 cm⁻¹. The state has 0⁺ character, and dissociates to I⁺ + F⁻ in the diabatic approximation.     

The emission spectrum of the 1B1(π*-n+) state of 1,2-cyclobutanedione excited at 488.0 nm

The spectrum of the emission from the ¹B₁(π^*-n₊) state of 1,2-cyclobutanedione excited at 488.0 nm has been measured. Wavelengths and vibrational assignments are reported for 24 bands between 490 and 550 nm, 12 of which can be identified with hot bands in the absorption spectrum. Prominent bands in the emission spectrum are associated with excitation of V^''₈, the symmetric in-plane carbonyl bend (281 cm⁻¹); v^''₁₂, the asymmetric carbonyl wag (488 cm⁻¹); and v^''₇, a symmetric ring distortion (522 cm⁻¹). Sequences in v₁₃, the ring-twisting vibration, are also prominent; the initial excitation lies in the 13³₃ absorption band, while the emission shows intensity maxima for v^'₁₃ = 0 and 2, and a bimodal vibrational relaxation is suggested.     

Jahn—Teller effects in substituted benzene cations. III. Gas phase emission spectrum of sym-C6Cl3H+3

The gas phase emission spectrum of 1, 3, 5-C₆Cl₃H⁺₃ was obtained in a discharge tube. Vibronic analysis involving correlation of ion fundamental frequencies with those of parent molecules enables a detailed comparison to be made between the vibrational structure of the spectrum of the trichloro-ion and that of 1, 3, 5-C₆F₃H⁺₃. Analogous Jahn—Teller effects are shown to take place in the ground state of the two ions. The same linear coupling model is used and two possible solutions for D₆ and ω₆ are obtained by fitting the first two intervals in the 6^0,0_{v$\text{1}\text{2}$} progression in 1, 3, 5-C₆Cl ₃H⁺₃: (i) D₆ = 0.05 - 0.08, ω₆ = 455 - 447 cm^?1, (ii) D₆ = 0.39 - 0.49, ω₆ = 399 - 392 cm^?1. Arguments based on previously established criteria, and applied here to the case of the 1, 3, 5-C₆Cl₃H⁺₃ ion are given to select set (ii) as being far more satisfactory in interpreting the experimental data. Fitting to a larger number of bands gave D₆ = 0.45, ω₆ = 395 cm^?1. The Jahn—Teller potential energy barrier E^JT₆ = 178 cm^?1 is about three times greater than in the 1, 3, 5-trifluorobenzene ions, but sufficiently small for the dynamic Jahn—Teller effect to be operative in 1, 3, 5-C₆Cl₃H⁺₃. Some remarks are made concerning assignments in the excitation spectrum and matrix fluorescence analyses.     

Asymmetric torsional potential function and conformational analysis of furfural by far infrared and Raman spectroscopy

The far i.r. (400-50 cm⁻¹) spectra of gaseous and solid furfural (2-furancarboxaldehyde), c-C₄H₃O (CHO), have been recorded. Additionally, the Raman (3500-20 cm⁻¹) spectra of the gas and liquid have been obtained at variable temperatures and the spectrum of the solid at 25 K. These data have been interpreted on the basis that the molecule exists in two different conformations in the fluid states and that the conformation which has the two oxygen atoms oriented in a trans configuration, OO-trans, is most stable (ΔH ⩽ 1 kcal/mol) in the gas; however, the conformation which has the two oxygen atoms oriented cis, OO-cis, is preferred in the liquid (ΔH = 1.07 ± 0.03 kcal/mol) and is the only rotamer present in the spectra of the solid. The asymmetric torsional fundamental for the OO-trans rotamer has been observed at 146.25 cm⁻¹ in the far i.r. spectrum of the vapor and has five accompanying “hot bands”. The corresponding fundamental for the OO-cis rotamer has been observed at 127.86 cm⁻¹ along with a “hot band” which occurs at 127.46 cm⁻¹. From these data a cosine-based potential function governing internal rotation of the CHO top has been determined and the potential coefficients have values of V₁ = 173 ± 2, V₂ = 3112 ± 20, V₃ = 113 ± 2 and V₄ = −198 ± 6 cm⁻¹. This potential is consistent with an enthalpy difference between the more stable OO-trans and high energy OO-cis conformers being 286 ± 24 cm⁻¹ (818 ± 67 cal/mol) and a trans to cis barrier height of 3255 ± 20 cm⁻¹ (9.31 ± 0.06 kcal/mol). These results are compared to the corresponding quantities obtained previously from microwave spectroscopy and theoretical methods.     

The ab initio calculation of the band origin and vibrational frequencies of the Ã-X̃ system of HNCl using the non-rigid bender hamiltonian

A three-dimensional fit of ab initio MRD CI potential data has been made for the lowest two electronic states of the HNC1 molecule (X̃ ²A″ and à ²A'), and the corresponding vibrational frequencies and rotational energies have been computed using the non-rigid bender Hamiltonian. For the ground state the vibrational frequencies obtained are ν₁ = 2942 cm⁻¹, ν₂ = 1232 cm⁻¹, and ν₃ = 549 cm⁻¹, while the corresponding values for the first excited state are 3524,947 and 836 cm⁻¹ respectively. We calculate T_c(à ²A') 16200 cm⁻¹, T_o(òA') = 16400 cm⁻¹, and the Franck-Condon maximum, Ã(0,3,1)-X̃(0,0.0), is calculate at 19200 cm⁻¹(5200 Å).     

Highly resolved polarized absorption spectra of single-crystal [Ru(bpy)3](PF6)2

Polarized absorption spectra of neat single-crystal [Ru(bpy)₃](PF₆)₂ at 300 and 5 K are presented. The spectra show pronounced vibronic structure and it is possible to assign the vibrations to known Raman frequencies. Furthermore, the different electronic states corresponding to the vibronic transitions are identified and assigned. The assignment of the lowest excited states - observed in absorption - agrees with an earlier classification of the emitting states. In particular, the E ⊥ c-polarized transition A'₁ ⇌ 2E' (classified in D'₃), at 17816 cm⁻¹, is found at the same energy (experimental error: ± 1 cm⁻¹) in emission and absorption and represents a zero-phonon, zero-vibron transition. The low-energy part of the E¦¦_c-polarized spectrum (below ≈ 24000 cm⁻¹) is not dominated by a series of different electronic states but by a 1600 cm⁻¹ progression with zero-vibron transition at 18770 cm⁻¹.     

Ir absorption spectrum of CrO2Cl2 molecules for high-lying states of the vibrational quasi-continuum

A new approach to the spectroscopy of highly excited vibrational states of polyatomic molecules has been elaborated. The molecules of CrO₂Cl₂ were prepared in states with a vibrational energy of the ground electronic term A₁ of ≈ 19000 cm⁻¹ by means of internal conversion of electronic energy from the electronic state B₁ excited by laser radiation. The spectroscopy of the vibrationally excited molecules has been carried out in the region of the ν₆ and ν₁ bands with diode and CO₂ lasers. The fwhm of the obtained spectrum was ≈ 15 cm⁻¹. The intermode interaction in CrO₂Cl₂ has been theoretically analyzed, and the calculated spectrum compared with that measured experimentally. The time evolution of the spectrum of vibrationally excited CrO₂Cl₂ molecules has been studied. The average energy transferred per one collision with unexcited CrO₂Cl₂ molecules was equal to 〈δE〉 ≈ 1200 cm⁻¹.     

Vibrational spectra of cyanosubstituted cyclopropanes—III. Cyanocyclopropane and cyanocyclopropane-1-d1

The vibrational spectra of cyanocyclopropane have been reinvestigated with the gas phase i.r. spectrum reported for the first time. The i.r. spectra of cyanocyclopropane-1-d₁ have been measured from 4000 to 200 cm⁻¹ in the liquid and the gaseous phases and from 4000 to 400 cm⁻¹ in the polycrystalline state. Raman spectra of the liquid down to 50 cm⁻¹ were obtained. A vibrational assignment of all fundamentals is proposed. With the present data, we had to reassign several fundamentals published in the literature.     

Combined microwave-optical barrier determination for molecules with a heavy symmetric internal top: CF3NO and CF3CHO

The torsional data for CF₃NO have been rein vest igated. A model with a single degree of freedom and three adjustable parameters is sufficient to fit data to v = 8 in the electronic ground state. For CF₃NO we obtain F_o = 1.9822(42) cm⁻¹, V₃ = 238.4(1.6) cm⁻¹ and V₆ = −5.8(1.6) cm⁻¹ or F_o = 1.9894(66) cm⁻¹,F₃= −0.194(55) cm⁻¹ and V₃ = 239.3(1.9) cm⁻¹. A similar treatment for CF₃CHO gives F_o = 1.97(14) cm⁻¹, V₃ = 305(25) cm⁻¹ and V₆ = −8.7(1.2) cm⁻¹. A need for a re-examination of the torsional fundamental is indicated for CF₃CHO. These studies support the general conclusion that for a heavy internal top the internal rotation constant, F_o, required to fit a range of torsional splittings is different from that calculated from structural considerations alone. The difference indicates a large change in F with torsional averaging.     

Quenching of I(2P½) by R-OH compounds. Influence of the alkyl group on the quenching efficiency

The deactivation of I(²P_½) by R-OH compounds (R = H, C_nH_2n+1) was studied using time-resolved atomic absorption at 206.2 nm. The second-order quenching rate constants determined for H₂O, CH₃OH, C₂H₅OH, n-C₃H₇OH, i-C₃H₇OH, n-C₄H₉OH, i-C₄H₉OH, s-C₄H₉OH, t-C₄H₉OH, are respectively, 2.4 ± 0.3 × 10⁻¹², 5.5 ± 0.8 × 10⁻¹², 8 ± 1 × 10⁻¹², 10 ± 1 × 10⁻¹², 10 ± 1 × 10⁻¹², 11.1 ± 0.9 × 10⁻¹², 9.8 ± 0.9 × 10⁻¹², 7.1 ± 0.7 × 10⁻¹², and 4.1 ± 0.4× 10⁻¹² cm³ molec⁻¹ s⁻¹ at room temperature. It is believed that a quasi-resonant electronic to vibrational energy transfer mechanism accounts for most of the features of the quenching process. The influence of the alkyl group and its role in the total quenching rate is also discussed. © 1997 John Wiley & Sons, Inc.     

The reactions of some interstellar ions with benzene,cyclopropane and cyclohexane

The reactions of the cyclic molecules C₆H₆ (benzene), c-C₃H₆ (cyclopropane) and c-C₆H₁₂ (cyclohexane) with ArH⁺ (ArD⁺), H₃⁺, N₂H⁺, CH₅⁺, HCO⁺, OCSH⁺, C₂H₃⁺, CS₂H⁺ and H₃O⁺ have been studied at 300 K using a SIFT apparatus. All the reactions except those of C₂H₃⁺ proceed via proton transfer and all are fast except the H₃O⁺ and CS₂H⁺ reactions with c-C₆H₁₂ which are endothermic and which establish that the proton affinity of c-C₆H₁₂ is 160 ± 1 kcal mol⁻¹, which is considerably lower than the published value. In the c-C₃H₆ and the c-C₆H₁₂ reactions multiple products are observed and hence “breakdown curves” for the protonated molecules are constructed and the appearance energies of the various ion products are consistent with available thermochemical data. The reactions of C₂H₃⁺ with these cyclic molecules are atypical within this series of reactions in that they appear to proceed largely via hydride ion transfer. The implications of the results of this study to interstellar chemistry are alluded to.     

Infrared and raman spectra,conformational stability,barriers to internal rotation,ab initio calculations and vibrational assignment of difluoroacetyl chloride

The Raman (3100–10 cm⁻¹) and infrared (3100–30 cm⁻¹) spectra of difluoroacetyl chloride, CHF₂CClO, in the gas and solid phases have been recorded. Additionally, the Raman spectrum of the liquid with qualitative depolarization ratios has been obtained. From these data, a trans/gauche equilibrium is proposed in the gas and liquid phases, with the trans conformer (hydrogen atom eclipsing the oxygen atom and trans to the chlorine atom) the more stable form in the gas, but the gauche rotamer is more stable in the liquid and is the only form present in the annealed solid. From the study of the Raman spectrum of the gas at different temperatures, a value of 272 ± 115 cm⁻¹ (778 ± 329 cal mol⁻¹) was determined for ΔH, with the trans conformer the more stable form. Similar studies were carried out on the liquid and a value of 109 ± 9 cm⁻¹ (312 ± 26 cal mol⁻¹) was obtained for ΔH, but now the gauche conformer is the more stable form. A potential function for the conformational interchange has been determined with the following potential constants: V₁ = 397 ± 23, V₂ = −101 ± 5, V₃ = 474 ± 3, V₄ = −50 ± 3, and V₆ = 10 ± 2 cm⁻¹. This potential has the trans rotamer more stable by 179 ± 31 cm⁻¹ (512 ± 89 cal mol⁻¹) than the gauche conformer. A complete vibrational assignment is proposed for both conformers based on infrared band contours, Raman depolarization data, group frequencies and normal coordinate calculations. The experimental conformational stability, barriers to internal rotation, and fundamental vibrational frequencies are compared with those obtained from ab initio Hartree-Fock gradient calculations employing both the RHF/3-21G^* and RHF/6-31G^* basis sets, and to the corresponding quantities obtained for some similar molecules.     

The vibrational spectrum and normal coordinate analysis of chlorodifluoromethane,CHClF2

The vibrational spectrum of chlorodifluoromethane has been reexamined. The i.r. and Raman spectra of the three isotopic species, ¹²CHClF₂, ¹³CHClF₂ and ¹²CDClF₂, have been obtained with better accuracy and higher resolution than in previous work. An SCF ab initio geometry optimization and quadratic force field calculation have been performed, and this force field has been further optimized to best fit the observed frequencies. The absorption spectrum of the ν₄, 2ν₆ region has been recorded at high resolution (0.002 cm⁻¹) and an analysis of the Fermi resonance perturbation has been carried out.     

Infrared spectrum of gaseous carbonyl fluoride-18O

From the infrared spectra of gaseous carbonyl fluoride-¹⁸O(F¹²₂C¹⁸O) the six fundamental vibrational frequencies (in cm⁻¹) are: (a₁) 1895.2 (average of Fermi resonance doublet), 947.3, 576.5; (b₁) 1242.3, 604.9; (b₂) 770.0. These unambiguous assignments are consistent with the less certain assignments for this isotopic species that Mallinson, McKean, Holloway and Oxton, Spectrochim. Acta 31A, 143 (1975) derived from an argon-matrix spectrum of 4% F¹²2 C¹⁸O in a mixture of four isotopomers.     

The crystal and molecular structure of 5,5-diphenyloctafluorogermanthrene, (C6H5)2GeC12F8

F---F steric interaction between the two 6,6′-fluorines of the C₆F₄ rings in C₁₂F₈Ge(C₆H₅)₂ cause quite distortions in the molecule as these two fluorine atoms are forced to within 2.419 Å of each other (Van der Waals distance ⋍ 2.7 Å). Crystal data: C₁₂F₈Ge(C₆H₅)₂, M_r 522.89, C2/c, a 29.065(2), b 8.066(2), c 23.000(3) Å, β 129.85°, U 4139.63 ų, Z = 8, D_x 1.678 Mg m⁻³, Mo-K_α, λ 0.7107 Å, μ 15.58 cm⁻¹, F(000) = 2064, T 293 K, R = 0.044 for 2264 reflections with I > 3σ(I); Δϱ ± 0.5 e⁻