The ground-state dipole moment of Bal from high-precision stark spectroscopy

The electric dipole moment of the X²σ⁺ state of Bal was measured using the molecular-beam laser-microwave double-resonance technique. From the analysis of the splitting and shift of rotational transitions in an electric field, the dipole moment of the vibrational ground state was determined as μ = 5.969(6) D (absolute error of the measurement in parentheses). The dipole moment predicted from an ionic bonding model is 6.14 D.     

The electronic absorption spectrum and excited state dipole moment of 3-fluoropyridine

The electronic absorption spectrum of 3-fluoropyridine in the vapour state and in solutions in different solvents in the region 3000-1900 Å has been measured and analysed. Three systems of absorption bands; n→π* transition I, π→π* transition II and π→π* transition III are identified. The oscillator strength of the absorption band systems due to the π→π* transition II and π→π* transition III and the excited state dipole moments associated with these transitions have been determined by the solvent-shift method.     

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.     

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.     

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.     

State-selected dissociation of cis-HONO(Ã A″): Effect of intramolecular hydrogen bonding

The influence of intramolecular hydrogen bonding on the photodissociation of cis-HONO is probed via measurements on the OH fragment ejected by specific ---N=0 stretching (ν₂) vibrational levels of the à state. Due to hydrogen bonding between the H atom and the terminal oxygen, the ν₂ motion is coupled to the in-plane HON bend ν₃. Since the latter evolves into fragment rotation, the rotational energy and anisotropy of the OH product increases with the number of ν₂ quanta. By contrast, ν₂ in trans HONO is a relatively isolated ---N=O vibration and thus does not influence the OH photofragment's properties.     

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 dipole moment in the lowest singlet pi formed from pi state of indole determined by the optical Stark effect

Abstract— A Stark effect is observed in the rotational fine structure of the 0–0 band of the lowest π*π state of indole. This yields a dipole moment change |Δμ_A| = 0·14±0·05. D. Evidence is presented which indicates that the sign of Δμ_A is positive. An increase of dipole moment on excitation is in agreement with the value (+ 0·06 D) corresponding to the previously calculated orbitals of Song and Kurtin. The direction of the transition moment, calculated from the results of rotational analysis published by Mani and Lombardi, is found to be 26° from the molecular A-axis.     

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 A2 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 ³A₂- 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.     

Dipole moment of cis-glyoxal in the 1B1 electronic state from static and modulated stark spectroscopy

The Stark effect on the ¹B₁ - ¹A₁ transition of cis-glyoxal near 487.5 nm is investigated. The effect arises from interaction between appropriate pairs of accidentally degenerate rotational levels. By using static and modulated electric fiels a value of 2.3 ± 0.5 D for the dipole moment along the b-axis of the molecule in the ¹B₁ state is obtained.     

The resonance Raman spectrum of tetramethylbutadiene in its lowest excited triplet state

The resonance Raman spectrum of tetramethylbutadiene in its lowest excited triplet state, with a reported lifetime of 80 ns, is presented. The triplet state was produced by laser flash photolysis using acetone as sensituer in acetonitrile. Transient Raman bands were seen at 1620, 1395, 1353, 1275, 1239, 1048, and 521 cm⁻¹.     

First-order stark effect and electric dipole moment of H3P … HC15N by pulsed-nozzle fourier-transform microwave spectroscopy

The first-order Stark effect in the J = 4 ← 3, K = 1 transition of the weakly bound dimer H₃P … HC¹⁵ N has been obeserved and measured by pulsed-nozzle Fourier-transform microwave spectroscopy under the selection rules ΔM = O and ΔM = ± 1. The electric dipole moment μ= 4.046(47) D determined for H₃P … HC¹⁵ N has been interpreted in terms of an enhancement Δμ = 0.60 D on dimer formation.     

Laser optogalvanic spectroscopy of N2 from the AΣu metastable state in a corona excited supersonic expansion

A hollow cathode combined with a corona excited supersonic expansion has proven to be an efficient method of producing a stable discharge in a N₂/Ar gas mixture. A high-resolution and rotationally cold absorption spectrum of the well-known (2,0) and (8,7) bands of the B³Π_g ← A³Σ_u⁺ first positive system of N₂ was recorded. It illustrates the sensitivity of the laser optogalvanic detection technique coupled to such an apparatus. A significant reduction of the linewidth and an enhancement of the signal-to-noise ratio were obtained. A high variational excitation process has been observed and is discussed.     

Determination of dipole moment in the ground and excited state by experimental and theoretical methods of N-nonyl acridine orange

The absorption and fluorescence spectra of N-nonyl acridine orange are determined at room temperature (298 K) in cyclohexane, benzene, carbon tetrachloride, chloroform, chlorobenzene and dichloromethane. The ground state of dipole moment was obtained by impedance measurements using Guggenheim-Debeye's method. The experimental excited state dipole moment of N-nonyl acridine orange was determined using Bakhshiev's and Kawski-Chamma-Viallet's formulae and solvent polarity parameter proposed by Reichardt. These experimental results were completed with theoretical results using quantum chemical methods. The experimental (muexp=10.76 D) and theoretical (mucal=9.9 D) dipole moments in the ground and excited state (muexp*=14.56 D) were compared.     

Microwave—optical double resonance in the B 3Π0+ excited state of ICl

Pure rotational transitions were observed in the electronically excited state B ³Π₀⁺ of ICl. This state was populated by optical pumping with a single-mode dye laser. From the observed spectrum precise values of the quadrupole hyperfine coupling constant cqQ of iodine and the effective rotational constant were derived for both isotopes I ³⁵Cl and I ³⁷Cl.     

Predissociation of acetylene in à Au state

The fluorescence excitation spectrum, the MPI spectrum, and the absorption spectrum of acetylene due to the à ¹A_u← transition were observed in a gas and in a supersonic jet. A sudden decrease in the fluorescence quantum yield Φ_f was found above the V⁴ K² (46339 cm⁻¹) vibronic sublevel. The decrease is due to predissociation into C₂H + H. AK and J dependence on Φ_f was also found.     

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.     

Measurement of the sixth overtone band of nitric oxide, and its dipole moment function, using cavity-enhanced frequency modulation spectroscopy

We applied cavity-enhanced frequency modulation absorption spectroscopy (also known as noise-immune cavity-enhanced optical heterodyne molecular spectroscopy) to perform high-resolution spectroscopy of the sixth overtone band of nitric oxide near 797 nm. By using novel high-bandwidth balanced detectors, baseline variations caused by residual amplitude modulation were significantly reduced. The ultrahigh sensitivity (2 x 10(-10) cm(-1) minimum detectable absorption at 1 Hz detection bandwidth) of our spectrometer allowed accurate measurements of 15 individual line intensities of P- and R-branch transitions in the 2Pi(1/2)-2Pi(1/2) subband. A vibrational transition moment of 3.09(6) muD+/-13% and Herman-Wallis coefficients of a = -0.0078(26) and b = 0.001 25(45) were found by fitting the line intensities. Based on our measured transition moment, and those of other transitions from the literature, a new parametrization for the electric dipole moment function (EDMF) of nitric oxide, valid for 0.91 < or = r < or = 1.74 A, has been extracted. The residuals of this fit demonstrate that the derived EDMF is the most accurate representation to date of the dipole moment function. The new EDMF will be valuable for accurate intensity prediction of transitions that cannot be easily measured experimentally.     

Selective excitation effects in microwave optical double resonance and phosphorescence spectroscopy of molecular crystals

The photoexcitation routes used to produce molecular crystal, triplet states are shown to have important optical and microwave spectral consequences. 2-benzoylpyridine crystals at 4.2 K have T₁ → S₀ phosphorescence spectra showing line width dependence on whether initial production of the T₁ state is through direct T₁ → S₀ absorption, or through S₁ ← S₀ absorption followed by S₁ → T₁ intersystem crossing. Striking differences are seen in the optically detected zero-field resonance spectra.