Radical Cation of 2,5-Dimethyl-2,4-hexadiene:  Resonance Raman Spectrum and Molecular Orbital Calculations

Balakrishnan, Gurusamy; Offersgaard, Jesper Falden; Wilbrandt, R.

doi:10.1021/jp992071u

Cited by 3 publications

(7 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In contrast, the beat pattern was easily detected in the plateau range of the electron-transfer product state, i.e., in the ionized perylene chromophore. Beat patterns due to wave-packet motion have been observed before in the plateau range of electron-transfer product states in the case of homogeneous electron-transfer reactions. , It is known for other aromatic molecules that differences in vibrational frequencies are often small between neutral and ionized molecules. − The transient absorption curve of the ionized perylene chromophore in the DTB−Pe molecule attached to TiO 2 was recorded at 575 nm (part A of Figure ). Strong oscillations appeared toward the plateau of the curve.…”

Section: Resultsmentioning

confidence: 83%

Experimental Fingerprints of Vibrational Wave-Packet Motion during Ultrafast Heterogeneous Electron Transfer

et al. 2001

View full text Add to dashboard Cite

By application of 20 fs laser pulses, vibrational wave packets of low-energy modes (mainly 357 and 421 cm-1) were generated in the perylene chromophore that gave rise to periodic beats that lasted longer than 1 ps in transient absorption signals. Electron transfer from the excited singlet state of the perylene chromophore, attached as molecule DTB−Pe via the −CH2−phosphonic acid group to anatase TiO2, was measured in ultrahigh vacuum with a time constant of 75 fs. The vibrational wave packet that was generated in the donor state continued its motion for several hundred femtoseconds in the product state of the reaction, i.e., in the ionized chromophore. This is direct proof for electron transfer occurring from a nonrelaxed vibrational population that was created by the short laser pulse in the donor molecule. The rise of the product state showed a staircase-like time dependence. The steps are attributed to electron transfer that occurs preferentially each time the vibrational wave packet (frequency 480 cm-1) reaches a crossing point for the potential curves of reactant and product state. Such wave-packet modulation of heterogeneous electron transfer can arise if the density of electronic acceptor states in the electrode is changing strongly over an energy range on the order of the reorganization energy below the excited molecular donor orbital.

show abstract

Section: Resultsmentioning

confidence: 83%

Experimental Fingerprints of Vibrational Wave-Packet Motion during Ultrafast Heterogeneous Electron Transfer

et al. 2001

View full text Add to dashboard Cite

show abstract

“…Two very strong Raman bands were observed at 1668 and 1658 cm 1 and assigned as an overtone (2 19 ) and C C stretching mode ( 5 ), respectively. Similarly, the medium-intensity band recorded at 1627 cm 1 34 in the infrared spectrum of the liquid is assigned to C C stretching (B u ) whereas a combination band was measured at 1684 cm 1 (Tables 3 and 4); the same fundamental is observed at 1630 cm 1 for the 2,4-dimethyl-1,3-pentadiene molecule. 45 Generally, the earlier vibrational assignments 3,4 are satisfactory to a large extent except for few cases will be discussed in detail.…”

Section: Vibrational Assignmentsmentioning

confidence: 84%

“…A g (2868 and 488 cm 1 ), B g 759 cm 1 and B u (753 and 674 cm 1 ). However, none of the unscaled and/or scaled wavenumbers obtained from the MP2(full)/6-31G(d) basis set coincide or are even close to the aforementioned bands (Tables 3 and 4).…”

Section: Force Fields and Vibrational Wavenumbersmentioning

confidence: 99%

“…1,2 Moreover, the vibrational analysis of trans,trans-2,4-hexadiene (TTHD) is interesting for the general theory of hindered internal rotation around C-C bonds, which hypothetically results in six conformers with C 2h , C 2v and C s point groups. The infrared and Raman spectra of TTHD 3,4 reveal all the carbon skeleton to be planar (C 2h symmetry) along with normal coordinate analysis.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Vibrational analysis, conformational stability, force constants, barriers to internal rotations, RHF, MP2 and DFT calculations of trans,trans‐2,4‐hexadiene

Mohamed

Aly

2004

J Raman Spectroscopy

View full text Add to dashboard Cite

Six conformers are proposed for the trans,trans-2,4-hexadiene (TTHD) molecule. Utilizing the 6-31G(d) and 6-311+G(d) basis sets at the levels of RHF, MP2 with full electron correlation and DFT-B3LYP, five conformers are found to be transition states, due to the calculated imaginary wavenumber(s). Accordingly, the totally symmetric TTT conformer where the two methyl groups are staggered to all trans vinylic hydrogen's (C 2h symmetry) is the stable conformer in the gaseous, liquid and crystalline phases. Aided by MP2(full)/6-311+G(d) geometric parameters, a chosen value of the kinetic parameter F = 6.11284856 was determined. Utilizing the observed band at 148 cm −1 in the far-infrared spectrum of the gas, a value of 1.41 ± 0.06 kcal mol −1 was obtained for the C 3v internal rotor (V 3 ), compared with 1.83 ± 0.07 kcal mol −1 predicted from a potential energy surface scan (1 kcal = 4.184 kJ). Aided by normal coordinate analysis and quantum chemistry (QC) calculations, the scaled quantum mechanical (SQM) force field was obtained employing five scaling factors for different types of vibrational motions. The scaled vibrational wavenumbers from both MP2(full) and B3LYP levels using the 6-31G(d) basis set provides an excellent approach to the observed fundamentals in either infrared or Raman spectra of the TTT conformer. Thus, confident vibrational assignments and potential energy distributions (PEDs) were provided for all fundamental modes of the TTT conformer. Moreover, the conformational stabilities, structural parameters, rotational constants, infrared intensities and Raman scattering activities are also reported. These results are discussed and compared with the experimentally determined values for some related conjugate systems when appropriate.

show abstract

“…The DFT method was chosen because it is computationally less demanding than other approaches as regards inclusion of electron correlation. Moreover, in addition to its excellent accuracy and favorable computation expense ratio, the B3LYP calculation of Raman frequencies has shown its efficacy in numerous earlier studies by other researchers, often proving itself the most reliable and preferable method for many molecular species of intermediate size, including anions and cations …”

Section: Computational Methods and Experimental Systemmentioning

confidence: 99%

Density Functional Theory Used in Structure Determinations and Raman Band Assignments for Pseudoisocyanine and Its Aggregate

et al. 2002

View full text Add to dashboard Cite

We have performed quantum chemical calculations for the optimized structure and Raman vibrational frequenciessbased on density functional theory at the B3LYP level and using the 6-31G(dp) basis setsfor the cyanine dye cation 1,1′-diethyl-2,2′-quinocyanine, also referred to as pseudoisocyanine (PIC). We have ascertained that the equilibrium structure of ground-state PIC has near C 2 symmetry, with a 46°twist between the planes of the two quinoline moieties that are positioned about the central methine carbon. Vibrational mode analysis of the calculated Raman spectrum suggests that many of the experimentally observed Raman bands between 500 and 1800 cm -1 for monomeric PIC are associated with totally symmetric in-plane deformations of phenyl and/or pyridyl rings, while several weak bands below 500 cm -1 are attributed to out-of-plane doming and ruffling of quinoline macrocycles. We further have noted that (1) upon comparison of the Raman spectrum of PIC monomer with the Raman spectrum measured for aggregated PIC, under nonresonant condition, changes reveal that aggregation results in enhanced scattering for specific vibrational modes that contain principal contributions from in-plane deformation of the phenyl ring in the quinoline moiety; (2) with resonant excitation for the aggregate, observed vibrational modes associated with out-ofplane distortions of the quinoline macrocycle are found to exhibit even greater enhancement. Analysis of our Raman measurements for monomeric and aggregated PIC provides details about the structure of the molecular aggregate. Additionally, calculation of charge distribution, utilizing the Mulliken population analysis approach, indicates that positive and negative charges are alternately and symmetrically distributed over a conjugated ring system, and the positive charges among the peripheral hydrogens and those in the N-ethyl side chains are asymmetrically distributed.

show abstract

Radical Cation of 2,5-Dimethyl-2,4-hexadiene: Resonance Raman Spectrum and Molecular Orbital Calculations

Cited by 3 publications

References 22 publications

Experimental Fingerprints of Vibrational Wave-Packet Motion during Ultrafast Heterogeneous Electron Transfer

Experimental Fingerprints of Vibrational Wave-Packet Motion during Ultrafast Heterogeneous Electron Transfer

Vibrational analysis, conformational stability, force constants, barriers to internal rotations, RHF, MP2 and DFT calculations of trans,trans‐2,4‐hexadiene

Density Functional Theory Used in Structure Determinations and Raman Band Assignments for Pseudoisocyanine and Its Aggregate

Contact Info

Product

Resources

About