Raman spectroscopy from a picosecond-lived excited state of methyl orange

Vibrational Raman scattering from a picosecond-lived excited state of methyl orange in 9 N H₂SO₄ is reported. The vibrational frequencies of normal modes in ground and electronic excited states are separated by ≈ 10 cm^?1 but rather large differences exist in their intensities. In particular, the intensity of a mode at ≈ 1180 cm^?1, due to the NN stretch, is sensitive to the frequency of the nanosecond pulsed tunable laser. A bandwidth comparison between ground- and excited-state spectra reveals that the widths of bands of the latter, like that of the former are due to dephasing and other effects associated with interaction of molecules in the liquid phase.     

Photo-ionization of aromatic hydrocarbon negative ions in ethers. The biphenyl anion

On the basis of Marcus' theory of electron transfer the mechanism and kinetics of electron ejection from lower excited states of aromatic hydrocarbon negative ions in liquid ethers are discussed.The application of the theory to the photo-ionization of biphenyl^? in glymes by nanosecond ruby laser pulses studied by Makkes van der Deyl et al. leads to a free energy of electron ejection for the ground state ion, ΔG⁰_e ≈ 12000 cm^?1.     

Matrix Raman studies of Bin(n ⩾ 2) molecules

Resonance Raman spectra of bismuth molecules reveal two progressions with ω_e = 172 and 152 cm^?1 The metal concentration dependence allows us to assign the 172 cm^?1 band to Bi₂ and the 152 cm^?1 band to a larger molecule, most likely Bi₄. Thus the existence of an X' ground state of Bi₂ ≈ 1500 cm^?1 below the X state can be excluded.     

On triplet exciton trapping in 1,4-dibromonaphthalene

From the study of triplet exciton trapping in 1,4-dibromonaphthalene it appears that several optically accessible excitons can exist with excitation energies within 1 cm^?1 and lifetimes differing by two orders of magnitude. Furthermore trap-like states exist ≈ cm^?1 below the exciton band. Delayed fluorescence arises from annihilation between an exciton and the very shallow trap-like state.     

Reexamination of the phosphorescence of Ba2Pt2(H2P2O5)4 via thermally modulated emission spectroscopy

Reexamination of the phosphorescence of Ba₂Pt₂(H₂P₂O₅)₄ reveals that the ≈10 K spectrum is a superposition of two electronic transitions [³A₂u(E_u,A_1u → A_1g] separated by ≈40 cm^?1. Each band displays a prominent 110 cm^?1 vibrational progression. Franck-Condon analysis yields a ≈0.25 Å distortion of the PtPt bond in the excited states, interpreted as a contraction.     

Thermal decomposition kinetics of bisthiourea cadmuim(II) tetrathiocyanato diammine chromate(III)

Cadmium thiourea reinickate undergoes two-stage thermal decomposition on heating. The DTG peak temperatures are 291 and 469°C and the corresponding DTA temperatures are 255 and 490°C. The kinetic parameters for the first stage decomposition are E* ≈ 120kJ mole^?1; Z ≈ 1.2 × 10⁸ cm³ mole^?1 sec^?1 and ΔS* ≈ ?95 J mole^?1 K^?1. For the second stage, E* ≈ 133 kJ mole^?1; Z ≈ 6.1 × 10⁵ cm^?1 mole^?1 sec^?1 and ΔS* ≈ ?142 J mole^?1 K^?1.     

Interpretation of the optical dephasing time and lineshape function in the S0 → T1 exciton transitions of 1,4-dibromonaphthalene

The lineshape function for the S₀ → T₁ absorption in 1,4-dibromonaphthalene (DBN) is analyzed in terms of exchange theory. It is shown that the dominant optical dephasing mechanism for the electric dipole transition to the k = 0 state in the band results from the absorption and emission of a low energy optic phonon. This process dephases the optical absorption because of frequency differences of the phonon in the ground and excited state. In addition, it is shown how to extract the energy of the phonon responsible for dephasing, the phonon absorption rate, and the lifetime in the phonon promoted state from the data. The analysis of the data for DBN shows that very little dephasing of the optical transition occurs before ≈ 15 K but from 15 K to ≈ 40 K the singlet-triplet transitions to site I (20192 cm^?1) and site II (20245 cm^?1) are dephased by absorption and emission of an ≈ 38 cm^?1 and 45 cm^?1 phonon respectively. The phonon absorption rates by the k = 0 state in the exciton band are similar for both sites being 5 × 10⁶ s^?1 and 3 × 10⁵ s^?1 at 4 K and 7 × 10¹¹ s^?1 and 4 × 10¹¹ s^?1 at 30 K for site I and II respectively. Finally, the lifetimes in the phonon promoted state for sites I and II are 0.23 and 0.28 ps over the range 15–40 K.     

Optical studies of the electronphonon interaction in the pyrene-PMDA complex

Low temperature phosphorescence spectra of pyrene-PMDA (pyromellitic acid dianhydride) imbedded in a naphthalene-PMDA host crystal are reported. The spectra exhibit resolved zero-phonon and multi-phonon structure which is significant since the phosphorescent state is characterized by ≈36% charge-transfer character. Several different phonons contribute to the structure with the dominant phonon having ground and excited state (from hot band analysis) frequencies of 25 and 15 cm^?1. The linear electronphonon coupling strength for the 25cm^?1 phonon is computed. This phonon is tentatively assigned to rotational motion of the rigid complex. Linewidth data yield a relaxation time of 0.4 ps at 2 K for the 25 cm^?1 phonon which is believed to be a pseudolocalized or resonant mode.     

Intermediate level structure in the s2 state of the isolated ultracold ovalene molecule

Spectroscopic information pertaining to interstate coupling between the S₂ and S₁ electronic states of ovalene, whose electronic origins are separated by ≈ 1800 cm^?1, has been obtained by the interrogation of the fluorescence action spectrum and of the energy-resolved fluorescence in seeded supersonic beams.     

Theoretical study of electronic structure of rhodium mononitride and interpretation of experimental spectra

Potential energy curves of 22 electronic states of RhN have been calculated by the complete active space second‐order perturbation theory method. The X¹Σ₀⁺ is assigned as the ground state, and the first excited state a³Π₀+ is 978 cm^?1 higher. The ¹Δ(I) and B¹Σ⁺ states are located at 9521 and 13,046 cm^?1 above the ground state, respectively. The B¹Σ⁺ state should be the excited state located 12,300 cm^?1 above the ground state in the experimental study. Moreover, two excited states, C¹Π and b³Σ⁺, are found 14,963 and 15,082 cm^?1 above the X¹Σ⁺ state, respectively. The transition C¹Π₁–X¹Σ₀⁺ may contribute to the experimentally observed bands headed at 15,071 cm^?1. There are two excited states, D¹Δ and E¹Σ⁺, situate at 20,715 and 23,145 cm^?1 above the X¹Σ⁺ state. The visible bands near 20,000 cm^?1 could be generated by the electronic transitions D¹Δ₂–a³Π₁ and E¹Σ⁺₀–X¹Σ⁺₀ because of the spin–orbit coupling effect. © 2013 Wiley Periodicals, Inc.     

On the low-lying states of TiC

The ground and low-lying excited states of TiC are investigated using a CASSCF—externally contracted Cl approach. The calculations yield a ³Σ⁺ ground state, but the ¹Σ⁺ state is only 780 cm^?1 higher and cannot be ruled out. The low-lying states have some triple bond character. The nature of the bonding and origin of the states are discussed.     

Electronic structure and vibrational frequency of Cr2

Cr₂ is produced by pulsed YAG laser vaporization of chromium metal and its fluorescence excitation spectrum is analyzed. The high value of vibrational frequency ΔG″_{$\text{1}\text{2}$} = 452.34 cm^?I (ω″^e ≈ 470 cm^?1) and short internuclear distance r″_e = 1.6788 Å are indicative of a very strongly bound ¹∑⁺_g ground state.     

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.     

Microwave spectrum of cyclohexanone

The rotational spectrum of cyclohexanone has been observed within the frequency region from 18.0 to 40.0 GHz. Transitions in the ground state and six excited states have been assigned. The ground state rotational constants are (in MHz) A = 4195.316 +- 0.059, B = 2502.627 ± 0.005 and C = 1754.443 ± 0.005.From information obtained from relative intensity measurements, these excited states are estimated to be ~ 100 cm^?1 above the ground state for the first excited state of the ring-bending mode and ~ 180 cm^?1 for the first excited state of the ring-twisting mode.     

Ultrafast transient processes of monomers,dimers, and aggregates of pseudoisocyanine chloride (PIC)

Pulses at 17450 cm^?1 absorbed at the peak of the aggregate band are very effective for photobleaching. The large absorption cross sections of the aggregates are ≈ 10^?14 cm². But at 18920 cm^?1 intensities three orders of magnitude higher are required for a significant reduction of transmission. Dimers appear to dissociate under strong illumination.     

Investigation of the excimer dynamics in 9,10-dichloroanthracene crystals using picosecond spectroscopy

The dynamics of excimer formation, excimer migration, and excimer dissociation in β-9,10-dichloroanthracene crystals were investigated by means of picosecond time-resolved fluorescence spectroscopy. In the temperature range from T = 20 K to T = 40 K we were able to temporally resolve the relaxation into the excimer state. The excimer formation rates were determined to be k ≈ 1.8 × 10¹¹ s^?1 at T = 40 K and k ≈ 2.0 × 10¹⁰ s^?1 at T<30 K. The excimer migration was investigated by measuring the excimer annihilation rate as a function of temperature. At room temperature 20% of the excimers are dissociated. The excimer binding energy is estimated to be B = 1360 cm^?1. The experimental results are explained in terms of a kinetic scheme comprising the population and depopulation of exciton, trap, and excimer states. The nature of the trap state is identified and it is shown that thermal activation of a 25 cm^?1 librational mode induces the relaxation of the trap into the excimer state.     

A consistent model for the thermal decomposition of NCN3 and the singlet– triplet relaxation of NCN

The thermal decomposition of cyanogen azide (NCN₃) and the subsequent collision‐induced intersystem crossing (CIISC) process of cyanonitrene (NCN) have been investigated by monitoring excited electronic state ¹NCN and ground state ³NCN radicals. NCN was generated by the pyrolysis of NCN₃ behind shock waves and by the photolysis of NCN₃ at room temperature. Falloff rate constants of the thermal unimolecular decomposition of NCN₃ in argon have been extracted from ¹NCN concentration–time profiles in the temperature range 617 K <T< 927 K and at two different total densities: k(ρ ≈ 3 × 10^?6 mol/cm³)/s^?1=4.9 × 10⁹ × exp (?71±14 kJ mol^?1/RT) (± 30%); k(ρ ≈ 6 × 10^?6 mol/cm³)/s^?1=7.5 × 10⁹ × exp (‐71±14 kJ mol^?1/RT) (± 30%). In addition, high‐temperature ¹NCN absorption cross sections have been determined in the temperature range 618 K <T< 1231 K and can be expressed by σ /(cm²/mol)= 1.0 × 10⁸ ?6.3 × 10⁴ K^?1 × T (± 50%). Rate constants for the CIISC process have been measured by monitoring ³NCN in the temperature range 701 K <T< 1256 K resulting in k_CIISC (ρ ≈ 1.8 ×10^?6 mol/cm³)/ s^?1=2.6 × 10⁶× exp (‐36±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 3.5×10^?6 mol/cm³)/ s^?1 = 2.0 × 10⁶ × exp (?31±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 7.0×10^?6 mol/cm³)/ s^?1=1.4 × 10⁶ × exp (?25±10 kJ mol^?1/RT) (± 20%). These values are in good agreement with CIISC rate constants extracted from corresponding ¹NCN measurements. The observed nonlinear pressure dependences reveal a pressure saturation effect of the CIISC process. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 30–40, 2013     

Exchange interactions in a trigonal chromium (III) dimer. Optical spectroscopy of tris-(μ-hydroxo)-bis-[(1,4,7-trimethyl-1, 4,7-triazacyclononane) chromium(III)] triperchlorate

High-resolution absorption, luminescence, Zeeman and MCD experiments were performed on single crystals of the title compound. The singlet-triplet and triplet-quintet exchange splittings in the ground state are 138 and 267 cm^?1, respectively. The corresponding exchange parameters are 2J= ?128 cm^?1 and j = 1.6 cm^?1. The zero-field splitting in the ground level is ?2.25 cm^?1. The lowest-energy emitting state is a ³E state, split into four spinor components with a total spread of 8 cm^?1.     

Darstellung,Eigenschaften und elektronische Raman-Spektren von Bis(chloro)phthalocyaninatoferrat(III), -ruthenat(III) und -osmat(III)

Preparation, Properties and Electronic Raman Spectra of Bis(chloro)-phthalocyaninatoferrate(III), -ruthenate(III) and -osmate(III) Bis(chloro)phthalocyaninatometalates of Fe^III, Ru^III and Os^III [MCl₂Pc(2-)]^?, with an electronic low spin ground state are formed by the reaction of [FeClPc(2-)] resp. H[MX₂Pc(2?)] (M = Ru, Os; X = Cl, I) with excess chloride in weakly coordinating solvents (DMF, THF) and are isolated as (n-Bu₄N) salts. The asym. M? Cl stretch (ν_as(MCl)) is observed in the f.i.r. at 288 cm^?1 (Fe), 295 cm^?1 (Ru), 298 cm^?1 (Os), ν_as(MN) at 330 cm^?1 (Fe), 327 cm^?1 (Ru), and 317 cm^?1 (Os); only ν_s(OsCl) at 311 cm^?1 is resonance Raman (r.r.) enhanced with blue excitation. The m.i.r. and FT-Raman spectra are typical for hexacoordinated phthalocyanines of tervalent metal ions. The UV-vis spectra show besides the characteristic π-π* transitions (B, Q, N, L band) of the Pc ligand a number of extra bands at 12–15 kK and 18–24 kK due to trip-doublet and (Pc→M)CT transitions. The effect of metal substitution is discussed. The r.r. spectra obtained by excitation between the B and Q band (λ₀ = 476.5 nm) are dominated by the intraconfigurational transition Γ₇ Γ ₈ arrising from the spin-orbit splitting of the electronic ground state for Fe^III at 536 cm^?1, for Ru^III at 961 cm^?1 and Os^III at 3 028 cm^?1. Thus the spin-orbit coupling constant increases very greatly down the iron group: Fe^III (357 cm^?1)< Ru^III (641 cm^?1)< Os^III (2 019 cm^?1). The Γ₇ Γ ₈-transition is followed by a very pronounced vibrational finestructure being composed in the r.r. spectra by the coupling with ν_s(MCl), δ(MClN) and the most intense fundamental vibrations of the Pc ligand. In absorption only vibronically induced transitions are observed for the Ru and Os complex at 1 700-2800 rsp. 3100-5800 em^?1 instead of the 0-0 phonon transitions. The most intense lines are attributed to combinations of the intense odd vibrational mo-des at ≈ 740 and 1120 cm^?1 with ν₅(MCI), δ(MClN).     

A molecular electronic Raman effect of the ferricenium ion

A molecular electronic Raman effect is reported for the ferricenium ion. The transitions occur at 213 cm^?1 and 1580 cm^?1 to spin-orbit levels of the ground electronic configuration (a_1g)²(e_2g)³. The positions of the spin-orbit states as obtained from the Raman spectrum agree with EPR data.