The electronic spectra and excited state dipole moment of 2-fluoropyridine

The electronic absorption spectrum in the vapour state and in solution in different solvents in the region 3000–1900 Å and the fluorescence and phosphorescence emission spectra in ethanol or cyclohexane at 77 K have been studied for 2-fluoropyridine and analysed. Two systems of absorption band corresponding to the π→π* transition II and π→π* transition III have been observed and the excited state dipole moments have been determined from the solvent-induced shifts of the electronic absorption bands. The half-life of phosphorescence in cyclohexane at 77 K is found to be 3.5 s.     

Electronic absorption spectrum and excited state dipole moment of 2,6-difluoropyridine

The u.v. absorption spectrum of 2,6-difluoropyridine in the region 41 000-34 000 cm⁻¹ in the vapour state and in solution has been recorded and a vibronic analysis made. Only one system of bands arising from the π → π* transition has been observed and the 0,0 band is located at 37 840 cm⁻¹ in the vapour-phase spectrum. The oscillator strength of the band system in solution and the dipole moment in the excited state associated with the transition were determined.     

Study of the electronic spectra of 2-fluoro-5-chloropyridine and determination of the excited state dipole moment

The ultraviolet absorption spectrum in the region 300-190 nm in the vapour phase and in solution in different solvents, and the luminescence emission spectra in ethanol and cyclohexane at 77 K have been measured for 2-fluoro-5-chloropyridine and analysed. The molecule shows two systems of absorption bands corresponding to the π→π* transition II and π→π* transition III. The oscillator strength of the two systems of absorption bands in solutions and the excited state dipole moment in the ¹π, π* state have been determined. The half-life of phosphorescence in cyclohexane is measured and found to be 3·6 s.     

The study of dipole moment of some substituted acetic acids in an electronically excited state

The electronic absorption spectra of eight substituted acetic acids have been measured at room temperature in several solvents. The ground state dipole moments are evaluated experimentally for these molecules. These ground state values are used in conjunction with the spectral results to evaluate their first electronically excited state dipole moments. For all the molecules investigated here the dipole moments in the excited state are higher than their ground state values.     

The microwave spectrum and dipole moment of 1,1-diflurobenzocyclopropene

The rotational spectrum of 1,1-difluorobenzocyclopropene, measured in the X- and R-bands, has been analysed to give the rotational constants in the ground and first four vibrational states. These constants are in agreement with a structure based on those of crystallographically determined related molecules. Indirect evidence is adduced that the carbon skeleton is indeed planar. The dipole moment in the ground (3.57₂ ± 0.02 D) and first excited state (3.54 ± 0.03 D) has been determined through an analysis of the second-order Stark effect. This high value implies considerable polarisation of the π-electron framework.     

Microwave spectrum and dipole moment of norbornane

The microwave spectrum of norbornane has been studied in the 26–40 GHz region. The rotational constantsA = 3694.246 MHz B = 3212.566 MHz, C = 2774.813 MHz and the dipole moment μ = 0.091(8) D have been determined. These values are compared with electron diffraction data.     

Determination of the excited state dipole moment of fluorenone using the method of solvatochromism

The absorption spectra and steady state fluorescence spectra of fluorenone have been obtained at room temperature for various concentrations in a series of non polar and polar solvents. The concentration effect shows two fluorescence bands, one at shorter wavelength due to monomer and another at longer wavelength due to excimer formation by triplet-triplet annihilation process. The excited state dipole moments of both monomer and dimer are calculated by the method of solvatochromism. A reasonable agreement has been observed between the values obtained by the method of solvatochromism and electrochromism.     

Solvent effects on the absorption and fluorescence spectra of coumarins 6 and 7 molecules: determination of ground and excited state dipole moment

Absorption and fluorescence emission spectra of coumarins 6 and 7 were recorded in solvents with different solvent parameters, viz., dielectric constant epsilon and refractive index n. The fluorescence lifetime of these dyes were measured in butanol at higher values of viscosity over temperature. Experimental ground and excited state dipole moments are determined by means of solvatochromic shift method and also the excited state dipole moments are determined in combination with ground state dipole moments. It was determined that dipole moments of the excited state were higher than those of the ground state in both the molecules.     

Microwave spectrum and dipole moment of 1,2,3,4-tetra-fluorobenzene

The microwave spectrum of the ground state of 1,2,3,4-tetrafluorobenzene has been measured in the range 7 to 25 GHz. A possible structure of the molecule is discussed. The rotational constants obtained are (in MHz): A = 2090.711 ± 0.012, B = 1196.257 ± 0.014, C = 760.880 ± 0.005. The observed inertial defect, Δ = 0.010 amu Ų, confirms the planar structure. A dipole moment of 2.42 ± 0.05 Debye was determined.     

Microwave spectrum and dipole moment of glycolic acid

More than 200 rotational transitions of glycolic acid (CH₂OHCOOH) have been assigned in the frequency range 18–40 GHz. Rotational constants and centrifugal distortion constants for the ground state and two vibrationally excited states were deduced. From Stark splittings the dipole moment was determined: μ_a = 1.913(5), μ_b = 0.995(14) and μ_total = 2.156(9) D.     

The microwave spectrum,structure and dipole moment of 1,4-pentadiyne

The microwave spectra of 1,4-pentadiyne and 1,4-pentadiyne-1,5-d₂ are assigned and rotational and centrifugal distortion constants obtained. A unique structure could not be determined. However, analysis of the moments of inertia indicates that the bond distances in C₅H₄ are close to typical values found in other related compounds. An interaction involving the acetylene moieties is evidenced by the derived bond angles. The data are consistent with either the central CCC angle being close to the tetrahedral value with the acetylene groups pushed away from linearity by approximately 3–4° or opening of the central CCC angle to about 113° along with linear acetylene groups. A range of structures between these two is also possible. The dipole moment is determined to be 0.516(5) D.     

Comments on the determination of excited state dipole moment of molecules using the method of solvatochromism

The present note comments on several publications which appeared in different journals containing many inaccurate statements and lacking honest citations of basic papers dealing with the application of solvatochromism to determine excited state dipole moments.     

Determination of the dipole moment of thioformaldehyde in the a3A2 excited state by laser phosphorescence excitation spectroscopy

Doppler-limited phosphorescence excitation spectra have been recorded at various electric fields for two rotational transitions in the $\text{a}$³A₂-$\text{X}$¹A₁ 0-0 band of H₂CS. Stark splittings were resolved, and were used to determine the dipole moment in the excited electronic state. The value found, 0.57(3) D, is of the order expected by comparison with dipole moments determined for other states of H₂CS, but rather lower than that predicted by ab initio calculations.     

Microwave spectrum,structure and dipole moment of trimethylamine-borane

The ground state rotational spectra often isotopic species of trimethylamineborane, (CH₃)₃N¹⁰BH₃, (CH₃)₃N¹¹BH₃, (CH₃)₃N¹⁰BD₃, (CH₃)₃N¹¹BD₃, (CH₃)₃N¹¹BD₂H, (CD₃)₃N¹⁰BH₃, (CD₃)₃N¹¹BH₃, (CD₃)₃N¹⁰BD₃, (CD₃)₃N¹¹BD₃ and (¹³CH₃)(¹²CH₃)₂N¹¹BH₃, have been measured and the effective moments of inertia obtained. The utilization of Kraitchman's equations leads to an r_s value of the B-H distance of 1.211±0.003 Å and a NBH angle of 105.32±0.16°. By a least squares fit of the rotational constants the following structural parameters were obtained: r(NC) = 1.495 Å, r(BN) = 1.609 Å, and ∠BNC = 110.9°. The value of the dipole moment was found to be 4.59±0.13 D. A lower limit to the barrier to internal rotation of the BH₃ group was determined to be 3.4 kcal/mole.     

Vibronic absorption spectra of acenaphthene in solution and its excited state electric dipole moments and polarizabilities

The vibronic spectra of acenaphthene in solution have been studied in detail in the region 27778–50000 cm⁻¹. A vibronic analysis of the two longest-wavelength absorption bands was made to reveal the vibrational modes that contribute to the enhancement of the intensities of these bands. The oscillator strengths of the various electronic transitions and the electric dipole moments and polarizabilities of several excited states were determined, the latter two by the solvent spectral frequency shift method.