Detection of SiF radicals with multiphoton ionization spectroscopy

We report the resonance enhanced multiphoton ionization spectrum of SiF between 430 and 492 nm. SiF radicals absorbed at least three photons to generate the observed m/z 47 SiF ions. Two-photon absorption bands from C″²Σ⁺ ← X ²Π, and C′²Π ← X ²Π, transitions were observed. An intense band from sequential one-photon transitions from the X ²Π_1/2(υ″ = 0) state through the A²Σ⁺ (υ′ = 0) and C″²Σ⁺ (υ′ = 1) states was observed.     

The A 1Π(u)←X 1Σ Electronic Transition of CCN+ and CNC+

The electronic absorption spectra of the A ¹Π_(u)←X ¹Σ transition of CCN⁺ and CNC⁺ have been observed in a 5 K Ne matrix after mass selection of C₂N⁺. CCN⁺ has the origin band at 462.0(2) nm. The vibrational structure with frequencies 1223(20) and 1725(20) cm⁻¹ corresponds to the symmetric and antisymmetric stretching modes in the excited state. The origin band of CNC⁺ is observed at 325.7(2) nm, and the system shows extensive vibrational excitation. Calculations of the potential energy functions of CCN⁺ and CNC⁺ in their X ¹Σ ground state and the A ¹Π state of CCN⁺ followed by variational evaluation of the rovibronic energy levels allows the assignment of the observed spectra. These spectroscopic data open the way to gas‐phase studies of the astrophysically important C₂N⁺ ions.     

Energy transfer processes in reactions of He(2 3S) and Ne(3P0,2) with CS2

A comparative spectroscopic study in the visible and ultraviolet ranges was conducted on the flowing afterglows resulting from the reactions of He(2 ³S) and Ne(³P_0,2) metastables with CS₂. Penning ionization was found to be the predominant energy transfer process. However, electron—ion recombination within the afterglows constitutes a major secondary process and gives rise to the most intense emitting system, CS(A ¹ Π → X ¹Σ⁺). Both afterglows were found to produce the CS⁺₂($\text{B}$²Σ⁺_u-$\text{X}$²Π_g), CS⁺₂($\text{A}$²Π_u-$\text{X}$²Π_g) and CS(a ³Π-X ¹Σ⁺) emission systems as well as some atomic sulfur emission lines. Some intensity differences were observed and are interpreted in terms of energetics and the formation mechanisms of the emitting species. A moderately strong CS⁺(A ²Π_i-X ²Σ⁺) emission system was also observed in the ehlium afterglow. In addition, a weak, sharp group of bands in the 390–420 nm range in the helium afterglow has been determined to be due to the presence of a small amount of He⁺ ions. This group of bands consists of two overlapping emission systems and are identified as CS(B ¹Σ⁺ → A ¹Π) and CS⁺(B ²Σ⁺ → A ²Π_i).     

CS+(B2Σ+ → A 2Πi) fluorescence from penning excitation of CS

The energy transfer reation of He(2³S) + CS was studied spectroscopically in a flowing afterglow apparatus. The CS⁺(B²Σ⁺ → A ²Π_i) transition is identified via three members of the Δν = 0 sequence (406–415 nm). The spin-orbit splitting of the (0, 0) band of CS⁺(A ²Π_i) is 301 ± 5 cm^?1. A weak emitting system (280–340 nm) is tentatively identified as CS⁺(B²Σ⁺→ X²Σ⁺).     

Emission spectra produced from thermal energy charge transfer reactions of Ar+ ions with CS and PN radicals

CS⁺(B²Σ⁺-A²Π_i) and PN⁺(B²Σ⁺-X²Σ⁺) emissions were observed for υ′ = 0 and 1 from argon afterglow reactions of CS and PN radicals. The rotational constant (B₀) of the CS⁺(B) state was estimated to be 0.696±0.002 cm^?1 from the difference between band head and band origin. The dependence of each emission intensity on the voltage applied to the ion-collector grids and on the argon pressure indicated that Ar⁺ was a plausible candidate. Vibrational populations of the CS⁺(B) and PN⁺(B) states obtained from the emission spectra shifted to lower vibrational levels in comparison with those expected from the energy resonance and Franck-Condon factors for ionization. This is explainable as the distortion of target radicals by approach of reactant ions.     

The kinetics of free radicals generated by IR laser photolysis. II. Reactions of C2(X 1Σ+g), C2(a 3Πu), C3(X̄ 1Σ+g) and CN(X 2Σ+) with O2

The 300 K reactions of O₂ with C₂(X ¹Σ⁺_g), C₂(a ³ Π_u), C₃(X? ¹Σ⁺_g) and CN(X ²Σ⁺), which are generated via IR multiple photon dissociation (MPD), are reported. From the spectrally resolved chemiluminescence produced via the IR MPD of C₂H₃CN in the presence of O₂, CO molecules in the a ³Σ⁺, d ³Δ_i, and e ³Σ^? states were identified, as well as CH(A ²Δ) and CN(B ²Σ⁺) radicals. Observation of time resolved chemiluminescence reveals that the electronically excited CO molecules are formed via the single-step reactions C₂(X ¹Σ⁺_g, a ³Π_u) + O₂ → CO(X ¹Σ⁺ + CO(T), where T denotes are electronically excited triplet state of CO. The rate coefficients for the removal of C₂(X ¹Σ⁺_g) and C₂(a ³Π_u) by O₂ were determined both from laser induced fluorescence of C₂(X ¹Σ⁺_g) and C₂(a ³Π_u), and from the time resolved chemiluminescence from excited CO molecules, and are both (3.0 ± 0.2)10^?12 cm³ molec^?1 s^?1. The rate coefficient of the reaction of C₃ with O₂, which was determined using the IR MPD of allene as the source of C₃ molecules, is <2 × 10^?14 cm³ molec^?1 s^?1. In addition, we find that rate coefficients for C₃ reactions with N₂, NO, CH₄, and C₃H₆ are all < × 10^?14 cm³ molec^?1 s^?1. Excited CH molecules are produced in a reaction which proceeds with a rate coefficient of (2.6 ± 0.2)10^?11 cm³ molec^?1 s^?1. Possible reactions which may be the source of these radicals are discussed. The reaction of CN with O₂ produces NCO in vibrationally excited states. Radiative lifetime of the ā ²Σ state of NCo and the ā ¹Π_u(000) state of C₃ are reported.     

Electronic,spectra, and spin orbit interaction for FrAr van der Waals system

The potential energy curves and spectroscopic constants of the ground and many excited states of the FrAr van der Waals system have been determined using a one‐electron pseudopotential approach. The Fr⁺ core and the electron–Ar interactions are replaced by effective potentials. The Fr⁺Ar core–core interaction is incorporated using the accurate CCSD(T) potential of Hickling et al. (Phys. Chem. Chem. Phys. 2004, 6, 4233). This approach reduces the number of active electrons of the FrAr van der Waals system to only one valence electron, which permits the use of very large basis sets for the Fr and Ar atoms. Using this technique, the potential energy curves of the ground and many excited states are calculated at the self consistent field (SCF) level. In addition, the spin–orbit interaction is also considered using the semiempirical scheme for the states dissociating into Fr (7p) and Fr (8p). The FrAr system is not studied previously and its potential interactions, spectroscopic constants and dipole functions are presented here for the first time. Furthermore, we have predicted the X²Σ⁺–A²Π_1/2, X²Σ⁺–AΠ_3/2, X²Σ⁺–B²Σ_1/2⁺, X²Σ⁺–3²Π_1/2, X²Σ⁺–3²Π_3/2, and X²Σ⁺–5²Σ_1/2⁺ absorption spectra. © 2012 Wiley Periodicals, Inc.     

Studies on the reaction N + N3 → N2(B 3Πg) + N2(X 1Σ+g)

Strongly enhanced N₂ first positive emission N₂(B ³Π_g → A ³Σ⁺_u) has been observed on addition of N atoms into a flowing mixture of Cl and HN₃. The dependence of the emission intensity on N atom concentration gave a rate constant for the reaction N + N₃ → N₂(B ³Π_g) + N₂(X ¹Σ⁺_g) of _i(1.6 ± 1.1) × 10^?11 cm³ molecule^?1 s^?1. That for the reaction Cl + HN₃ → HCl + N₃ is (8.9 ± 1.0) × 10^?13 cm³ molecule^?1 s^?1 from the decay of the emission. Comparison of the emission intensity in ClHN₃ with that in ClHN₃N gave the rate constant of the reaction N₃ + N₃ → N₂(B ³Π_g) + 2N₂(X ¹Σ⁺_g) as 1.4 × 10^?12 cm³ molecule^?1 s^?1 on the assumption that N + N₃ yields only N₂(B ³Π_g) + N₂(X ¹Σ⁺_g).     

High-resolution UV photoelectron spectrum of CO2

The highly-resolved HeI photoelectron spectrum of CO₂ is presented and its vibrational structure studied in detail. In the X? ²Π_g ionic state the v₃ antisymmetric mode is found to be excited in double quanta (v_1-v_2-v₃ = 0. 0. 2) with energy hv₃ = 181 meV. In the C? ²Σ_g⁺ state a single quantum of the same mode is found to be excited (hv₃ = 189 meV) in combination with a v₁ excitation. Vibronic interaction with vibrational levels in the B? ²Σ_u⁺ state of the ion is suggested to promote this (1, 0, 1) excitation. It is established that inelastic scattering processes contribute to the vibrational structure in the C? ²Σ_g⁺ band. The spin-orbit splitting in the X? ²Π_g is determined to be 19±1 meV and 10±2 eV in the ā²Π_u state. Vibronic structure is resolved in the X? ²Π_g band where the Renner-Teller coupling constant is determined to be ? = 0.21±0.02 and the vibrational energy of the v₂ mode as 60±7 meV. In the ā²Π_u state the v₂ energy is found to be hv₂ = 60 meV from the observed hot-band structure.     

Absolute emission cross sections for the calibration of optical detection systems in the 120–250 nm range

Absolute emission cross sections have been determined for electron impact on CO, NO and N₂. For the CO(A ¹ΠX ¹Σ⁺) and N₂(a ¹ΠX ¹Σ_g) radiation our data is in good agreement with that of other groups. For CO⁺ (B²Σ⁺X²Σ⁺) the values of the emission cross sections are different from those measured previously. This discrepancy is explained in terms of an inadequate straylight correction in the former experiments. For the NO(A²Σ⁺X²Π) emission no previous σ_em values are known to the authors. Furthermore the electronic transition moments of the NO(A²Σ⁺X²Π) and CO⁺(B²ΣX²Σ⁺) systems have been measured and are found to be independent of the internuclear distance.     

Chemiluminescent ion-molecule reactions in the system C+ + H2

The optical emission resulting from collisions between C⁺ ions and H₂ gas was measured in the energy range 2 to 20 eV_c.m.. The observed spectrum consists mainly of the CH⁺ A ¹Π → X ¹Σ⁺ band system; CH⁺ (A ^fΠ) is shown to be formed in the chemiluminescent reactio: C⁺(²P⁰) + H₂ → CH⁺(A ¹Π) + H(²S). The energy dependence of the emission cross section was measured. The occurrence of this reaction is discussed in terms of a electronic state correlation diagram for the system.     

Fluorescence of dissociating fragments from supersonic jet-electron collisions

Supersonically cooled jets of nitrogen, methane, ethane, cyclopropane, and azomethane are crossed with collimated streams of electrons. The CH (B²Σ^? → X²Π) spectra resulting from the electron-induced dissociation of CH₄, C₂H₆, and CH₂)₃ can be fit with rotation temperatures between 4000 and 6000 K for an electron energy of 100 eV. Flourescence spectra of N₂⁺ (B²Σ_w⁺ → X²Π) from the dissociative ionization of azomethane yield a rotational temperature of =8×10³ K; from ionization of molecular nitrogen the rotational temperature of B²Σ_w⁺ N₂⁺ is 45 K. Mechanisms for these various processes are discussed.     

Theoretical studies of molecular ions. Vertical ionization potentials of the nitrogen molecule

The ²Σ⁺_g, ²Π_u, and ²Σ⁺_u vertical ionization energies of nitrogen are obtained by using our theory of molecular electron affinities and ionization potentials, which permits the direct calculation of the ion-molecule energy differences. The contributions of charge redistribution and correlation energy change to the calculated ionization potentials are evaluated. The computational efficiency of the method is illustrated and comparisons are made with recent experimental results.     

O‐loss photodissociation of the OCS+ ion in the low‐lying electronic states studied using multiconfiguration second‐order perturbation theory

The CASPT2 potential energy curves (PECs) for O‐loss dissociation from the X²Π, A²Π, B²Σ⁺, C²Σ⁺, 1⁴Σ^?, 1²Σ^?, and 1⁴Π states of the OCS⁺ ion were calculated. The PEC calculations indicate that X²Π, 1⁴Σ^?, 1²Σ^?, and 1⁴Π correlate with CS⁺(X²Σ⁺) + O(³P_g); A²Π and B²Σ⁺ correlate with CS⁺(A²Π) + O(³P_g); and C²Σ⁺ probably correlates with CS⁺(X²Σ⁺) + O(¹D_g). The CASSCF minimum energy crossing point (MECP) calculations were performed for the C²Σ⁺/1⁴Σ^?, C²Σ⁺/1⁴Π, A²Π/1⁴Σ^?, A²Π/1²Σ^?, A²Π/1⁴Π, and B²Σ⁺/1²Σ^? state pairs and the spin‐obit couplings were calculated at the located MECPs. A conical intersection point between the B²Σ⁺ and C²Σ⁺ potential energy surfaces was found at the CASSCF level. Based on our calculations, seven O‐loss predissociation processes of the C²Σ⁺ state are suggested and an appearance potential value of 7.13 eV for the CS⁺ + O product group is predicted. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Die Photoelektron-Spektren der Dihalogen-acetylene

The photoelectron-spectra of the six dihaloacetylenes XC?CY with X, Y ? Cl, Br, I have been recorded. The first five bands of these spectra can be assigned (in order of increasing ionization potentials) to the states ²∏_(u)(1), ²∏_(g)(2), ²∏_(u)(3), ²∑_(g)⁺(4), ²∑_(u)⁺(5) where the lower indices g, u are valid only for the centro-symmetric molecules I(X, X). The first three states correspond to π-ionization, the last two to σ-ionization of the axially symmetrical lone pairs. The ²∏-states split under the influence of spin-orbit-coupling into components ²∏_3/2 and ²∏_1/2, the former having the lower energy. The assignment of states and components to the individual bands is confirmed by the size of the split due to spin-orbit-coupling, the vibrational fine structure of the bands and by a simple parametrization of the ZDO. molecular orbital model assumed as a basis for the qualitative discussion.     

Theoretical spectroscopic studies of InI and InI+

Relativistic configuration interaction calculations are carried out to study the electronic structure and spectroscopic properties of InI and InI⁺. Potential energy curves of the ground and a number of low‐lying states are constructed. Spectroscopic parameters of the bound states of both species are computed and compared with the experimental and other theoretical data. Effects of spin‐orbit coupling on the spectroscopic properties are studied. Because of the presence of the heavy atoms the effect is large. The spin‐orbit splitting of the ground state (X²Π) of InI⁺ is more than 8350 cm^?1. As a result of the strong spin‐orbit interaction between X²Π and A²Σ⁺ of InI⁺, the potential energy curve of A²Σ becomes repulsive. Radiative lifetimes for the spin‐forbidden transitions such as A³Π?X¹Σ and B³Π₁ ?X¹Σ of InI and spin‐allowed transitions such as B²Σ⁺?A²Σ⁺, C²Π?A²Σ⁺, and B²Σ⁺?X²Π are calculated. Vertical and adiabatic ionization energies of InI and the electric dipole moments of both the neutral and ionic species are estimated. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Observation and interpretation of the Li2 diffuse band in the region of 420 nm

We report the first observation of the Li₂ diffuse band in the region of 420 nm which is the analog of the diffuse bands in other alkali dimer spectra, for example, at 436.5 and 575 nm for the sodium and potassium cases, respectively. The observed diffuse band appears to arise from the 2³Π_g-1³Σ_u⁺ transition where the upper state corresponds to the 2p + 2p asymptote, and is subjected to the interesting configuration interaction with the potential curve of the ionic molecule Li^?(³P) + Li⁺(¹S) with the same symmetry. The origin of the 420 nm band is interpreted in terms of theoretical calculations of various Li₂ potential difference curves.     

Detection of nitrogen rotational distributions by resonant 2 + 2 multiphoton ionization through the a1Πg state

Characterization of laser 2 + 2 multiphoton ionization of nitrogen to obtain rotational state distributions has been investigated via the resonant two-photon transition a ¹Π_g(ν = 1) ← X ¹Σ_g(ν = 0). For room-temperature nitrogen, the spectral intensities and state distribution are directly related and give rotational temperatures of 290 ± 20 K. For power densities of 3 GW/cm², the ionization probability is 1 × 10⁻⁵ per N₂ molecule per average rotational state.     

Ab initio study of electronic energy transfer in the quenching of CO*(a 3Π) by H2

Potential energy calculations for the interaction of CO(a ³Π) with H₂(X ¹Σ_g⁺) are presented, both at the MC SCF level and with the inclusion of extensive configuration interaction. In C_2v geometry, the lowest two ³B₂ surfaces exhibit a strongly avoided crossing. At the highest level of theory used, the lowest surface provides a barrier-free adiabatic pathway for energy transfer from CO(a) to H₂, the products being CO(X ¹Σ⁺) and H₂(b ³Σ_u⁺), which dissociates to two H atoms. The energy transfer occurs by a two-electron exchange mechanism.     

Fluorescence spectra of laser-excited YO molecules in a H2O2Ar flame

CW dye laser induced fluorescence emission and thermal emission spectra of YO-molecules in a 1 atm H₂O₂Ar flame of 2430 K were recorded simultaneously. Narrow band laser excitation was applied to four rotational lines in the (1, 1) Q-branch of the A²Π_{$\text{3}\text{2}$}→X²Σ⁺ transition and broadband excitation was applied to several separate Q-branches of the A²Π_{$\text{1}\text{2}$,$\text{3}\text{2}$}→X²Σ⁺ transitions. From the differences between the fluorescence emission spectra and thermal emission spectra, we conclude that collisional de-excitation of an excited vibronic level takes place by vibrational relaxation, decay to the electronic ground state and by intermultiplet transfer in order of increasing probability.