H. Ding

Electronic spectra of the chains HC2nH (n=8–13) in the gas phase

The intense 1Σu+←X1Σg+ electronic transition of the chains HC2nH (n=8–13) has been recorded in the gas phase using resonant two color two photon ionization spectroscopy. The gas phase frequencies lie ∼1300 cm−1 to the blue of the values in a neon matrix. These polyynes appear to be linear in both the ground and the excited state and, as for the polyynes, spectral and theoretical evidence for large bond alternation in the ground state is found indicating localized π orbitals on the C≡C units. These species are the longest carbon chains observed spectroscopically in the gas phase up to now.

Gas phase electronic spectra of the linear carbon chains HC2n+1H (n=3-6,9)

The Bu200a3Σu−←Xu200a3Σg− transitions of HC13H and HC19H have been measured in the gas phase, exhibiting broad, Lorentzian shaped bands. More extensive Au200a3Σu−←Xu200a3Σg− spectra have been observed for HC2n+1H (n=3–6) than before with many new vibronic bands identified. The spectra were obtained by means of a mass selective resonant two-color two-photon ionization technique coupled to a supersonic plasma source. The electronic structures of this series of molecules (n=2–9) in both the ground and excited states have been investigated using DFT, MP2, and state-averaged CASSCF theories. The three lowest dipole allowed electronic transition systems are Au200a3Σu−←Xu200a3Σg−, Bu200a3Σu−←Xu200a3Σg−, and Cu200a3Πu←Xu200a3Σg−, located, for the smaller members of the series, in the visible, UV and VUV range, respectively. The Au200a3Σu−←Xu200a3Σg− system is found to be of medium intensity and the Bu200a3Σu−←Xu200a3Σg− transition is predicted to be very strong. This is a result of configuration mixing in the excited states. The oscillator strength of the lowest energ...

Gas phase electronic spectrum of C3H in the visible

The electronic spectrum of C3H has been observed by means of a resonant two color two photon ionization technique sampling a supersonic plasma source. On the basis of ab initio calculations, vibrational and rotational analysis, the complex vibronic system observed in the visible and near UV is assigned to three electronic transitions, Au200a2A′←Xu200a2Π, Bu200a2A″←Xu200a2Π and Cu200a2A″←Xu200a2Π of C3H. Potential curves along the CCH bending coordinate have been obtained because of its role for the electronic spectrum and dynamics of C3H.

Electronic spectra of the C2n+1H(n=2–4) radicals in the gas phase

The visible electronic spectra of the linear l-C2n+1H (n=2–4) radicals have been measured in the gas phase. These have been obtained by means of a mass-selective resonant two-color two-photon ionization technique coupled to a supersonic plasma source. The observed spectra are assigned to the Au200a2Δ←Xu200a2Π, Bu200a2Σ−←Xu200a2Π, and Cu200a2Σ+←Xu200a2Π electronic transitions arising from σ→π electron promotion. The assignments are based on ab initio calculations, wavelength dependence of the 000 transition on size, and isotopic substitution. The lifetime broadening of the bands and effects due to vibronic coupling are associated with the carbon skeleton bending modes. The detection of these carbon chains in the diffuse interstellar medium appears to be more favorable by radio astronomy rather than by electronic spectroscopy.

Diagnosis of a benzene discharge with a mass-selective spectroscopic technique

Abstract The products formed in a benzene discharge have been probed by resonant two photon ionization spectroscopy. The molecules formed are cooled in a supersonic expansion and mass-analysis combined with spectroscopic information is used to identify the species. By this means styrene, phenylacetylene, methylstyrene, indene, fluorene and tolane are recognized. No six-ring polycyclic aromatic hydrocarbon could be detected. With this method the plasma is sampled at an early stage where the ethynylated and cyclopentafused polycyclic aromatic hydrocarbons are more abundant than the more stable six-ring ones. The coupling of a discharge source to a REMPI detection system enables electronic spectra of neutral molecules to be obtained which can be used to study their role in combustion processes, plasmas as well as in astrophysics.

The gas phase spectrum of cyclic C18 and the diffuse interstellar bands

The gas phase spectrum of the cyclic C18 molecule recorded in the laboratory at a temperature typical of diffuse interstellar clouds is compared with absorption features towardOph and HD 204827 in the 5730-5934 8 region. For the origin band at 5928.5 8 an upper limit to the column density of � 1:8 ; 10 11 cm � 2 is inferred. The origin band pattern in the laboratory spectrum changes on lowering the internal temperature in the 100-20 K range and bears a striking resemblance to the observed structure of a number of DIBs at other wavelengths. This suggests that platelike molecules or ions, comprising a couple of dozen to hundred carbon atoms, could be responsible for some of the latter absorptions. Subject headingg ISM: general — ISM: lines and bands — ISM: molecules — stars: individual (� Oph, HD 204827)

Gas-phase electronic spectra of C18 and C22 rings

The electronic spectra of C(18) and C(22) in the 15 150-36 900 cm(-1) range have been detected in the gas phase by a mass-selective resonant two-color two-photon ionization technique coupled to a laser ablation source. The spectra were assigned to several electronic systems of monocyclic cumulenic isomers with a D(9 h) symmetry for C(18) and D(11 h) for C(22), based on time-dependent-density-functional calculations and reactivity with respect to H(2). The best cooling conditions were achieved with Kr as the buffer gas, and the origin of the A(1)A(2) ()<--X(1)A(1) () transition of C(18) at 592.89 nm shows a pair of 1 cm(-1) broadbands spaced by 1.5 cm(-1). The next electronic transitions exhibited much broader, approximately 30 (in the visible) to 200 cm(-1) (in ultraviolet range), features. The spectrum of C(22) exhibits an absorption pattern similar to C(18), except that the narrow features to the red are missing; the oscillator strength of the A<--X transition is predicted to be low.

Optical detection of C9H3, C11H3, and C13H3 from a hydrocarbon discharge source

Abstract Resonant two-color two-photon ionization spectra of C 9 H 3 , C 11 H 3 , and C 13 H 3 have been observed in the gas phase and are found to exhibit remarkably similar vibrational structure. All have origins in the 18,800–19,300xa0cm −1 region and a characteristic ≈40xa0cm −1 progression. Several pieces of spectroscopic information suggest a common moiety incorporating a strong, localized electronic transition, consistent with a low ionization potential as compared to other hydrocarbon radicals. Several possible structural motifs are discussed in relation to plasma, combustion and interstellar chemistry.

ELECTRONIC SPECTRA OF MgC2nH (n = 1-3) CHAINS IN THE GAS PHASE

Electronic transitions of MgC2nH (n = 1-3) have been observed in the gas phase in the visible region. A mass-selective, resonant two-color two-photon ionization technique, coupled with a laser ablation source, was used. Ab initio calculations of the geometries, energies, and vertical electronic excitations have been carried out using hybrid density functional theory and the coupled-cluster approach. The spectra are assigned as the A2Π ← X2Σ+ electronic transition of linear chains. The origin bands are located at 4383, 4453, and 4525 A for MgC2H, MgC4H, and MgC6H, respectively, and provide a means of detecting such species in astronomical environments.

Resonant two-photon ionization spectroscopy of BNB

Triatomic BNB has been produced by laser ablation of a boron nitride rod in a supersonic expansion of helium carrier gas and has been investigated using resonant two-photon ionization spectroscopy in the visible region. The B 2Pi(g)-X 2Sigma(u)+ band system has been recorded near 514 nm and is dominated by a strong origin band, which has been rotationally resolved and analyzed. Both the (11)B(14)N(11)B (64% natural abundance) and the (10)B(14)N(11)B (32% natural abundance) isotopic modifications have been analyzed, leading to the spectroscopic constants (and their 1sigma error limits) of B0(X 2Sigma(u)+)=0.466 147(70), B0(B 2Pi(g))=0.467 255(75), and A0(B 2Pi(g))=6.1563(38) cm(-1) for (10)B(14)N(11)B, corresponding to r(B-N)(X 2Sigma(u)+)=1.312 47(10) A and r(B-N)(B 2Pi(g))=1.310 92(11) A. Very similar values are obtained for the more abundant isotopomer, (11)B(14)N(11)B: B0(X 2Sigma(u)+)=0.444 493(69), B0(B 2Pi(g))=0.445 606(70), A0(B 2Pi(g))=6.1455(38) cm(-1), corresponding to r(B-N)(X 2Sigma(u)+)=1.312 41(10) A and r(B-N)(B 2Pi(g))=1.310 77(10) A. These results are discussed as they relate to Walshs rules and are compared to results for related molecules.