Vacuum Ultraviolet Absorption Spectra Research Articles

Stability of Di-imide

DI-IMIDE, HN = NH, as the prototype azo compound and an isoelectronic analogue of C2H4 and O2, is of great interest to the chemist. It is, however, generally considered to be so unstable as to have only a transient existence at ordinary temperatures1–3. Generated in situ in aqueous solution, it has been widely used in recent years as a reducing agent3, but has never been isolated or detected in these systems. It has been detected as a transient in the gas phase in several laboratories. Foner and Hudson4 produced di-imide by an electric discharge through flowing hydrazine vapour, detected it by mass spectrometry, and showed that it could be trapped at − 196° C and regenerated in the gas phase on warming. Trombetti5, in these laboratories, was able to measure the infrared and vacuum-ultraviolet absorption spectrum of the vapour in a similar flow system, and these two studies seemed to indicate a lifetime of at least a second or two. A brief account by Mock6 suggests that the lifetime might be much longer; he observed that when di-imide vapour together with ammonia and hydrazine was admitted to the inlet manifold of a mass spectrometer, a signal at m/e = 30 decayed with a half-life of several minutes and remained detectable for as long as 20 min. Uncertainty and lack of reproducibility of these observations led Mock to conclude only tentatively that di-imide might be as long lived as these data suggest.

Far-UV and photoelectron spectra of 1,3,5-trifluorobenzene

The photoelectron and vacuum-ultraviolet absorption spectra of 1,3,5-trifluorobenzene and its fully deuterated analog were measured. The two lowest ionisation potentials correspond to the π levels. We find two Rydberg series converging to the first IP and one converging to the second IP. The assignments are confirmed by the similarities between the vibrational fine structures of the photoelectron and the related Rydberg bands. These fine structures exhibit significant differences with respect to benzene.

A medium resolution study of aleene in the vacuum ultraviolet—I

Abstract A vacuum ultraviolet absorption spectra of gaseous allene was investigated with moderately high resolution down to 1160 A. Four broad, molecular bands were observed along with a large number of sharp peaks that are either vibrational or Rydberg in character. The vibrational separations were noted for the first three of the broad bands with averages of 580, 1100,1130, 960, 682 cm −1 and two major Rydberg series were found with Rydberg corrections of 0.92 and 0.37 converging to the same limit of 80,788 ± 25 cm −1 (10.016 ± 0.002 eV).

Vacuum ultraviolet absorption spectrum of carbonyl cyanide

Vacuum ultraviolet absorption spectrum of carbonyl cyanide

Electronic Spectroscopy of Maleimide and Its Isoelectronic Molecules. I. Maleimide and N-Alkylmaleimides

The electronic absorption spectra of maleimide and two N-alkylmaleimides are presented. Molecular-orbital classifications of four electronic transitions with energies 〈 6.5 eV are made for maleimide. Vibrational structure appearing in two of the transitions in the N-alkylmaleimides in the vapor phase is interpreted and assignments of the active vibrational modes discussed. A series of hot bands derived from the 2000-Å band of N-methylmaleimide is analyzed and employed in the association of the corresponding active ground- and excited-state vibrational modes. The vacuum-ultraviolet vapor absorption spectrum of N-methylmaleimide is presented. Phosphorescence emissions from maleimides in glassy media at 77°K suggest that the T1 states of these molecules are Γ n π*3.

The vacuum ultraviolet absorption spectrum of 1,1-dichloro-2,2-difluoroethylene

The vacuum ultraviolet absorption spectrum of 1,1-dichloro-2,2-difluoroethylene is reported. Two Rydberg progressions converging on an ionization potential of 9.69 ± 0.01 eV are described. The π* ← π (V ← N) transition energy (57471 cm −1) and ionization potential are discussed in terms of data for similar compounds.

Electron energy-loss spectra of some triatomic molecules

Electron energy-loss spectra in the range 3 to 20 eV of CO 2 , N 2 O, COS, CS 2 , SO 2 are reported. Rydberg series are compared with those identified in vacuum ultraviolet absorption spectra, and a number of new lowest members and new series are reported. The quantum defects of these are discussed in terms of the orbitals of the active electrons. CO 2 levels have been studied with variable scattering angle, the progressions around 15 eV showing characteristic forbidden transition behaviour, and being tentatively assigned as π 3 g σ g 1 II g and π 3 g σ g 3 II g . The generalized oscillator strength of CO 2 D ~ 11.09 eV shows a discrepancy from that reported by Lassettre & Shiloff (1965).

Vacuum-Ultraviolet Absorption Spectrum of Carbon Suboxide. II. The Effect of Low Temperature and the Effect of High Pressure of an Inert Gas on the 1780-Å Band

The gas-phase absorption spectrum of the 1780-Å band of carbon suboxide has been measured photo-electrically at both room and dry ice temperatures and in the presence of a high pressure of argon using a 1-m vacuum monochromator having a 1.0-Å bandwidth. The addition of 1500 psi of argon greatly broadens the vibrational structure and shifts the whole band to higher energies. On cooling from 298°K to 195°K, the size of the 14 vibrational bands on the 1780-Å transition remain unchanged relative to each other, but the intensity of the transition is decreased. The constancy in relative size of the vibrational bands at different temperatures rules out the possibility that they are a vibrational sequence in the 63-cm−1 ground-state πu bending mode and confirms their assignment as a progression in a 400-cm−1 excited-state bending vibration. The decrease in oscillator strength as the temperature is lowered and the regularity of the progression as it passes over the peak of the band imply that the linear–linear vertical transition is forbidden. The effect of the high pressure of argon on the 1780-Å band indicates that it is borrowing its intensity from a Rydberg band. The presence of a long progression in a bending mode is strong evidence that the equilibrium configuration in the excited state is nonlinear. The Herzberg–Teller theory of vibrationally induced electronic transitions and an INDO molecular orbital calculation have been used to assign the upper states of the 2650-, 1780-, and 1587-Å bands.

Spectrum of the CN molecule. I. Absorption in the vacuum ultraviolet

The vacuum ultraviolet absorption spectrum of CN is observed for the first time revealing a weak band system between 1490 and 1820 Å. Rotational and vibrational analysis shows the upper state to be the known E2Σ+ state. Four new vibrational levels are reported, resulting in the following molecular constants for the E state (cm−1):[Formula: see text]The strength of the absorption and its significance in astrophysics is discussed. The dissociation limits and the electron configurations of all known electronic states of CN are also discussed, and a tentative assignment of a previously unassigned 2Π state is proposed.

The quadrupole moment of NO +

From the analysis of the vacuum ultraviolet absorption spectrum of NO the quadrupole moment of NO +, in its ground state X 1Σ +, has been determined to be +0.79·10 −26 esu cm 2. A theoretical value of +0.62·10 −26 esu cm 2 has been calculated using LCAO-MO-SCF wave functions.

Excitation Energy Transfer in Alkanes. I. Exciton Model

The molecular exciton theory of sigma bonds, which was set up previously to explain the vacuum-ultraviolet absorption spectra of alkanes, is applied here to the primary radiation chemical reactions of linear and branched alkane polymers. From this a number of theoretical predictions are made, the most important being that very efficient excitation energy transfer will occur along the CC bonds of the polymer main chains without causing main chain scission but that excitation energy in CH bonds will be localized in pairs of these bonds and give rise here to a high rate of scission. These predictions are examined in detail in the following two papers, using experimental data.

Near infrared to vacuum ultraviolet absorption spectra and the optical constants of phthalocyanine and porphyrin films

Measurements are reported for photon energies between 0.5 and 11.8 eV of the absorption coefficient of thin films of free base, copper, and zinc phthalocyanines, chlorinated copper phthalocyanine, and free base protoporphyrin. Several new discrete transitions are observed in the ultraviolet spectra, in addition to a strong continuum component of absorption. The data covers a sufficiently extensive spectral range to permit the first determination of the spectral dependence of the optical constants for these materials.

Note on the3p54s3dConfiguration in Neutral Potassium (K i)

Intermediate coupling matrices for ${p}^{5}\mathrm{sd}$ were diagonalized with energy parameters based on restricted Hartree-Fock wave functions for K i $3{p}^{5}4s3d$. The resulting energies and Russell-Saunders percentage compositions for the levels are given. The baricenter of the configuration was taken as 170 644 ${\mathrm{cm}}^{\ensuremath{-}1}$, equal to the average energy relative to $3{p}^{6}4s$ as calculated by the Hartree-Fock method. Three autoionization lines previously observed in the vacuum ultraviolet absorption spectrum of K i are classified as transitions to levels of $3{p}^{5}4s3d$. An approximate correction of -2025 ${\mathrm{cm}}^{\ensuremath{-}1}$ to the above baricenter is thus obtained, and predicted positions for the other transitions to $3{p}^{5}4s3d$ are given. The doublet $3{p}^{6}4s^{2}S_{\frac{1}{2}}\ensuremath{\rightarrow}3{p}^{5}3d(^{1}P\ifmmode^\circ\else\textdegree\fi{})$ $4s^{2}P_{\frac{1}{2},1\frac{1}{2}}^{\ifmmode^\circ\else\textdegree\fi{}}$ (calculated position \ensuremath{\sim} 480 \AA{}) is predicted to absorb most of the oscillator strength of the array. The calculated percentage compositions of the levels confirm a conclusion of Sprott and Novick that the $^{4}D_{3\frac{1}{2}}$ level observed by them does not belong to $3{p}^{5}4s3d$. Calculated positions for $3{p}^{5}4s3d$ and $3{p}^{5}4s4p$ are consistent, within the approximations, with their conclusion that $3{p}^{5}4s3d^{4}F_{4\frac{1}{2}}^{\ifmmode^\circ\else\textdegree\fi{}}$ and $3{p}^{5}4s4p^{4}D_{3\frac{1}{2}}$ are not separated by more than \ensuremath{\sim} 0.15 eV.

Rydberg Progressions in cis- and trans-Butene

The far- and vacuum-ultraviolet absorption spectra of cis- and trans-butene and trans-butene-d8 have been recorded at low resolution. The more prominent bands are shown to be either the members of Rydberg series, ̄νn = 73 550 − R / (n − 1.03)2 (cis-butene), ̄νn = 73 650 − R / (n − 0.88)2 and ̄νn = 73 750 − R / (n − 0.24)2 (trans-butene), ̄νn = 73 900 − R / (n − 0.86)2 and ̄νn = 74 000 − R / (n − 0.23)2 (trans-butene-d8), or their vibrational subbands. The band observed at 49 690 cm−1 in trans-butene-d8 is seen, at higher resolution, to be polarized along the Z molecular axis, in agreement with its 3sR(Au) ← N(Ag) assignment. Finally, from a partial vibrational analysis of the trans-butene spectrum, the C=C and C–C bonds of the excited states are deduced to be slightly longer than in the ground state.

High resolution vacuum ultraviolet absorption spectra of the B1Σ+- X1Σ+, C1Σ+- X1Σ+, and i 3Σ+- X1Σ+ transitions in carbon monoxide

The C-X and B-X transitions in 12C16O and 13C16O have been studied under high resolution. Rotational analyses were performed on the (1–0) and (0–0) bands of both systems. Bands previously thought to be part of the B-X system have been assigned to an additional system, tentatively identified as j3Σ+-X1Σ+.

Vacuum ultraviolet absorption spectra of sublimed films of nucleic acid bases

AbstractMeasurements of the optical absorption spectra of the sublimed films of adenine, guanine, cytosine, thymine, and uracil were extended down to 120 mμ at room temperature. Several remarkable absorption peaks were found to exist below 190 mμ in addition to the already known ones near 260 mμ and 200 mμ. The intensities of these peaks were comparable to or, in some cases, even larger than those near 260 mμ and 200 mμ. It was found that the relative intensities of the absorption peaks differed considerably from sample to sample for all five bases, probably due to variation in the arrangement of the bases in the sublimed films. It was found also that the absorption spectra of the sublimed films change with aging on standing in vacuo at room temperature. On comparing the spectra of several fresh samples it was found that the intensities of the transitions with wavelength longer than 160 mμ of adenine, guanine, and uracil films are inversely correlated with those of the transitions shorter than 160mμ.

Vacuum-Ultraviolet Absorption Spectrum of Polystyrene

The vacuum-uv absorption spectrum of atactic and isotactic polystyrene is reported from 584 Å to onset of absorption at 2800 Å, and is compared with previous data from reflection and electron-energy loss measurements. Three of the electronic transitions in this region are assigned to excitations of the benzenering π electrons and the fourth to excitation of all the σ- and π-bonding electrons of the material; previous assignments of some transitions as due to collective excitations of free electrons are rejected. The spectrum of the solid is essentially as would be expected from gas-phase measurements apart from strong evidence of exciton interaction in one of the π-electron transitions.

Vacuum-Ultraviolet Absorption Spectrum of α,α,α-Trichlorotoluene

The vacuum-ultraviolet absorption spectrum of α,α,α-trichlorotoluene has been measured in the vapor phase by a recording vacuum-ultraviolet spectrophotometer, with which the absorption measurement has been extended down to 1600 Å. The spectrum of this compound was found to show considerably great difference in the vacuum-ultraviolet region from that of benzene in the sense that the A1g→E1u transition band of benzene splits into a doublet and a new band appears in the 1600–1700 Å region. Theoretical treatment was also carried out by calculating configuration interactions, on the assumption that electrons in a pseudo-π-molecular orbital, perpendicular to the benzene ring, formed from three C–Cl, conjugate with the π-electrons in the benzene ring. A good agreement was obtained between the experimental and the calculated results, and all the absorption bands observed in the present work have been interpreted well in terms of π→π* transition involving the intramolecular charge transfer. It has been concluded that the CCl3 group in α,α,α-trichlorotoluene has a strong electron donating character for the benzene ring.

Low-Energy, Large-Angle Electron-Impact Spectrum of Ethylene

The electron-impact spectrum of ethylene has been measured at primary energies of 35, 50, and 70 eV and a fixed scattering angle of 90°. The most intense inelastic peak was found to be at 8 eV. This peak corresponds to a number of unresolved allowed transitions which are observed in the vacuum-ultraviolet absorption spectrum. A peak was observed at 4.6 eV which was assigned to a forbidden singlet—triplet transition. The 6.5-eV ``ultraviolet mystery band'' transition was not observed. Neither was any peak observed in the spectrum which could be assigned to a large inelastic process at the ionization limit.

Vacuum ultraviolet absorption spectra of simple amides

Vacuum ultraviolet absorption spectra of six simple amides were measured. It was found that the positions of the firstπ→π * transition bands shift appreciably by the substitutions of methyl groups for hydrogen atoms of the NH2 and $$\begin{gathered} | \hfill \\ H - C = O \hfill \\ \end{gathered} $$ groups. A general tendency is that the substitution in the NH2 group shifts the band toward longer wavelengths, in the $$\begin{gathered} | \hfill \\ H - C = O \hfill \\ \end{gathered} $$ group however towards shorter wavelengths. This was explained satisfactorily by considering the nature of the band (intramolecular charge-transfer band) and the hyperconjugation effect of the methyl group.