Measurement of gas kinetic temperatures for polyatomic ions in inductively coupled plasma-mass spectrometry: Validation and refinements

The general method of comparing measured ion ratios to calculated ion ratios to determine a gas kinetic temperature (T_gas) is reviewed. Various mathematical refinements to the calculated partition functions are examined for their effect on the determined T_gas. It is found that (a) excited electronic states should be included for ArO⁺, neutral NO, and O₂; (b) a 10% error in solvent load, sample gas flow rate, vibrational constant (ω), rotational constant (B) or measured ion ratio produces only a 1 to 3% error in T_gas; (c) a 10% error in dissociation energy (D₀) creates nearly a 10% error in T_gas; and (d) high temperature corrections to the partition functions produce minimal change and can generally be neglected.     

High resolution studies of the origins of polyatomic ions in inductively coupled plasma-mass spectrometry,Part I. Identification methods and effects of neutral gas density assumptions,extraction voltage,and cone material

Common polyatomic ions (ArO⁺, NO⁺, H₂O⁺, H₃O⁺, Ar₂⁺, ArN⁺, OH⁺, ArH⁺, O₂⁺) in inductively coupled plasma-mass spectrometry (ICP-MS) are identified using high mass resolution and studied using kinetic gas temperatures (T_gas) determined from a dissociation reaction approach. Methods for making accurate mass measurements, confirming ion identifications, and correcting for mass bias are discussed. The effects of sampler and skimmer cone composition and extraction voltage on polyatomic ion formation are also explored. Neutral species densities at several locations in the extraction interface are estimated and the corresponding effects of the T_gas value are calculated. The results provide information about the origins of background ions and indicate possible locations for their formation or removal.     

Polyatomic ions in inductively coupled plasma–mass spectrometry: Part II: Origins of N2H and HxCO ions using experimental measurements combined with calculated energies and structures

Several polyatomic ions in inductively coupled plasma–mass spectrometry are studied experimentally and by computational methods. Novel calculations based on spin-restricted open shell second order perturbation theory (ZAPT2) and coupled cluster (CCSD(T)) theory are performed to determine the energies, structures and partition functions of the ions. These values are combined with experimental data to evaluate a dissociation constant and gas kinetic temperature (T_gas) value. In our opinion, the resulting T_gas value can sometimes be interpreted to deduce the location where the polyatomic ion of interest is generated. The dissociation of N₂H⁺ to N₂⁺ leads to a calculated T_gas of 4550 to 4900 K, depending on the computational data used. The COH⁺ to CO⁺ system yields a similar temperature, which is not surprising considering the similar energies and structures of COH⁺ and N₂H⁺. The dissociation of H₂CO⁺ to HCO⁺ leads to a much lower T_gas (< 1000 to 2000 K). Finally, the dissociation of H₂COH⁺ to HCOH⁺ generates a T_gas value between those from the other H_xCO⁺ ions studied here. All of these measured T_gas values correspond to formation of extra polyatomic ion in the interface or extraction region. The computations reveal the existence of isomers such as HCO⁺ and COH⁺, and H₂CO⁺ and HCOH⁺, which have virtually the same m/z values and need to be considered in the interpretation of results.     

Dissociation of polyatomic ions in the inductively coupled plasma

A general method for identifying the origin of a particular polyatomic ion is described. Based on a postulated dissociation reaction, measured ion signal ratios (e.g. Ar₂⁺/Ar⁺) are combined with mass bias corrections and estimates of the density of the neutral product (usually Ar, O or H atoms) to determine a gas kinetic temperature T_gas. The temperature can also be measured by the reduction in pressure when the ICP is sampled (compared to room temperature argon), or by other means. Dissociation energies and spectroscopic constants for the ions are necessary. For the particular instrument used, some of the findings of this study are: (a) ArO⁺ and ArN⁺ can be either dissociated (if the plasma potential is high) or created (if the plasma potential is low) by collisions between the sampler and skimmer; (b) the strongly-bound oxide ions O₂⁺ and MO⁺ for the rare earths are observed at levels consistent with T_gas ∼5300 K in a ‘hot’ plasma, but ClO⁺ is formed in excess; and (c) the abundances of most other polyatomic ions like H₂O⁺ and ArH⁺ correspond to higher densities than would be expected in the ICP itself.     

Theoretical study of electronic structure of rhodium mononitride and interpretation of experimental spectra

Potential energy curves of 22 electronic states of RhN have been calculated by the complete active space second‐order perturbation theory method. The X¹Σ₀⁺ is assigned as the ground state, and the first excited state a³Π₀+ is 978 cm^?1 higher. The ¹Δ(I) and B¹Σ⁺ states are located at 9521 and 13,046 cm^?1 above the ground state, respectively. The B¹Σ⁺ state should be the excited state located 12,300 cm^?1 above the ground state in the experimental study. Moreover, two excited states, C¹Π and b³Σ⁺, are found 14,963 and 15,082 cm^?1 above the X¹Σ⁺ state, respectively. The transition C¹Π₁–X¹Σ₀⁺ may contribute to the experimentally observed bands headed at 15,071 cm^?1. There are two excited states, D¹Δ and E¹Σ⁺, situate at 20,715 and 23,145 cm^?1 above the X¹Σ⁺ state. The visible bands near 20,000 cm^?1 could be generated by the electronic transitions D¹Δ₂–a³Π₁ and E¹Σ⁺₀–X¹Σ⁺₀ because of the spin–orbit coupling effect. © 2013 Wiley Periodicals, Inc.     

Potential energy and dipole moment of the Na2+ ionic molecule

The potential energy curves of 26 electronic states of ²Σ⁺_{g, u}, ²Π_{g, u}, and ²Δ_{g, u} symmetries of the alkali dimer Na₂⁺, dissociating up to Na(4d) + Na⁺, are investigated using an ab initio approach involving a nonempirical pseudopotential for the Na⁺(1s²2s²2p⁶) core and core‐valence correlation corrections. Furthermore, the transition dipole functions between many electronic states and vibrational energy spacings are presented. The spectroscopic constants of these electronic states are extracted and compared with the available theoretical and experimental results. A very good agreement is observed, especially, for the ground and the first excited states. However, the comparison between our study and the model potential (MP) calculations (Magnier and Masnnou‐Seeuws Mol. Phys. 1996, 89, 711) for several states has shown a clear disagreement. The MP well depths of the 3‐4²Σ⁺_g, 1²Π_g, 3‐4²Π_g, and 2²Π_u electronic states are largely underestimated. In addition, the 5‐7²Σ⁺_g, 3‐7²Σ⁺_u, 2²Π_g, 4²Π_g, and 1‐2²Δ_u MP electronic states are repulsive, although in this work, they are attractive with potential well depths of some hundreds of cm^?1. The data presented in this study are very useful for studies on ion–atom interaction and cold collision in the presence of electromagnetic fields. © 2013 Wiley Periodicals, Inc.     

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.     

Electronic states of Al2

Ab initio multi-configuration self-consistent field and first-order configuration interaction (FOCI) calculations in an extended basis set have been carried out for the lower energy electronic states of Al₂. The ten core electrons of each Al atom were replaced by an accurate compact effective core potential. The FOCI calculated T_o value for the ³Σ_g^?-³Σ_u^? transition agrees with the experimentally observed emission band to within 90 cm^?1. ³Π_u is calculated to be the electronic ground state of Al₂. Based on FOCI energies and qualitative intensity arguments, the reported optical absorption spectrum of matrix isolated Al₂ also agrees best with a ³Π_u ground state. The ³Σ_g^?1 state is calculated (T_e) at only 324 cm^?1 above the ³Π_u state, and the ¹ΣE_g⁺ state is predicted to lie higher.     

Case studies in multiphoton ionisation and dissociation of Na2

Dissociative ionisation of Na₂ via the 3s 3d ¹Σ _g and¹Π _g states has been studied in the near threshold energy regime up to 120 meV above the three particle (Na⁺ + Na(3s) +e ^?) break up limit. A pulsed, cold molecular beam, pulsed laser 2 colour 3 photon resonantly enhanced multiphoton ionisation, and kinetic energy analysis of the fragments by a time of flight method (KETOF) is used. As series of vibrational levels in the two intermediate 3s 3d Rydberg states are excited, slow Na⁺ fragments are observed with a maximum kinetic energy given by the excess energy of the 2 + 1 photon process above threshold, thus confirming a direct dissociative ionisation process. The intensity distribution of the Na⁺ fragments shows a very pronounced maximum at zero kinetic energy, its shape differing somewhat for the¹Σ _g and¹Π _g intermediate states. Also observed is a strong signal of fast fragments arising from a typical 4 photon process which leads to dissociation of Na ₂ ⁺ molecules in their electronic ground state.     

OH自由基的高精度量子化学研究

采用内收缩MRCI方法(Internally Contracted Multiconfiguration-Reference Configuration Interaction)研究了OH自由基, 计算得到其基态稳定构型的键长是0.09708 nm, 对应的实验值是0.096966 nm, 第一激发态的键长是0.10137 nm,实验值是0.10121 nm. 同时得到势能曲线PECs (Potential Energy Curve), 再分别由Murrell-Sorbie势能函数拟合计算和POLFIT程序计算得到OH自由基在基态X²Π和第一激发态A²Σ⁺时的光谱数据：平衡振动频率ω_e, 非谐性常数ω_eχ_e以及高阶修正ω_eY_e, 平衡转动常数B_e, 振转耦合系数α_e, 解离能D₀和垂直跃迁能量ν₀₀. 这些理论计算结果与最新的实验值非常吻合, 精确度比前人也有很大提高. 其中我们计算得到基态OH(X²Π)的解离能D₀＝35568.86 cm^－1, 第一激发态OH (A²Σ⁺)的解离能D₀＝18953.93 cm^－1, 从第一激发态A²Σ⁺ (ν＝0)到基态X²Π (v＝0)的垂直跃迁能ν₀₀＝32496.42 cm^－1.     

The energy balance and branching ratios associated with the chemiluminescent reaction Si(3P) + N2O(1Σ) → SiO*(a3Σ+, b3Π, A1Π) + N2(υ″ ⩾ 5) — possible formation of vibrationally excited N2

Silicon atoms react under single collision conditions with N₂O to yield chemiluminescent emission corresponding to the SiO a³Σ⁺?X¹Σ⁺ and b³Π?X¹Σ⁺ intercombination systems and the A¹Π?X¹Σ⁺ band system. A most striking feature of the SiN₂O reaction is the energy balance associated with the formation of SiO product molecules in the A¹Π and b³Π states. A significant energy discrepancy ( = 10000 cm^? = 1.24 eV) is found between the available energy to populate the highest energetically accessible excited-state quantum levels and the highest quantum level from which emission is observed. It is suggested that this discrepancy may result from the formation of vibrationally excited N₂ in a concerted fast SiN₂O reactive encounter. Emission from the SiO a³Σ⁺ (A¹Π) and b³Π(A¹Π, E¹Σ₀⁺) triplet-state manifold results primarily from intensity borrowing involving the indicated singlet states. Perturbation calculations indicate the magnitude of the mixing between the b³Π, A¹Π and E¹Σ₀⁺ states ranges between 0.5 and 2%. On the basis of these calculations, the branching ratio (excited triplet)/(excited singlet) is found to be well in excess of 500. An approximate vibrational population distribution is deduced for those molecules formed in the b³Π state. The present studies are correlated with those of previous workers in order to provide an explanation for diverse relaxation effects as well as observed changes in the ratio of a³Σ⁺ to b³Π emission as a function of pressure and experimental environment. Some of these effects are attributable to a strong coupling between the a³Σ⁺ and b³Π state. Based on the current results, there appears to be little correlation between either (1) the branching ratio for excited state formation or (2) the total absolute cross section for excited-state formation and (3) the measured quantum yield for the SiN₂O reaction. Implications for chemical laser development are considered.     

A theoretical study of the bound electronic states of the C−2 negative ion

Configuration interaction calculation are employed to study the X ²Σ⁺_g, A ²Π_u, B ²Σ⁺_u, ⁴Σ⁺_u and ⁴Δ_u states of the C^?₂ ion. The results are in good quantitative agreement with experimental findings for the Herzberg—Lagerquist (²Σ⁺_u-²Σ⁺_g) bands and predict a T_e value for the ²Π_u state of only 0.40 eV; corresponding transition moment results are obtained as a function of CC distance. The Cl electron affinity is 3.43 eV, in good agreement with the most recent experimental estimate for this quantity.     

Potential curves and molecular properties of Na2+

A model potential method in which a molecule is described as a single electron moving in the field of two polarizable cores is used to calculate the potential energy curves and the wavefunctions of the lowest six electronic states of the molecular ion Na₂⁺. The ground X²Σ_g state has a dissociation energy of 0.98 eV at an equilibrium separation of 3.3 Å and the excited ²Π_u state has a dissociation energy of 0.23 eV at an equilibrium separation of 5.2 Å. Various molecular properties of these two bound states are calculated. An analysis of the long range behaviour of all the six states is presented.     

Theoretical study of low‐lying electronic states of the LiRb+ molecular ion: Structure,spectroscopy and transition dipole moments

The electronic structure and the spectroscopic properties for low‐lying electronic states of the LiRb⁺ molecular ion, dissociating into Li (2s, 2p, 3s, 3p, 3d, 4s, and 4p) + Rb⁺ and Li⁺ + Rb (5s, 5p, 4d, 6s, 6p, 5d, and 7s), have been investigated using an ab initio approach based on non‐empirical pseudo potentials for the Li and Rb cores and parametrized l‐dependent polarization potential. We have determined the adiabatic potential energy curves and their spectroscopic constants for many electronic states of ²Σ⁺, ²Π, and ²Δ symmetries. A satisfying agreement, for the spectroscopic constants, has been obtained for the ground and the first excited states with the available theoretical works. Potential energy curves were presented, for the first time, for the higher excited states. In addition, we have localised and analysed the avoided crossings between electronic states of ²Σ⁺ and ²Π symmetries. Their existences can be related to the interaction between the potential energy curves and to the charge transfer process between the two ionic systems Li⁺Rb and LiRb⁺. Moreover, we have determined the transition dipole moments from X²Σ⁺ and 2²Σ⁺ states to higher excited states of ²Σ⁺ and ²Π symmetries. For our best knowledge, no experimental data on the LiRb⁺ molecular ion is available. These theoretical data can help experimentalists to optimize photoassociative formation of ultracold LiRb⁺ molecular ion and their longevity in a trap or in an optical lattice. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

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.     

Hermaphroditism in chemical dynamics: the reaction Ba + Cl2 → BaCl + Cl

The reaction Ba + Cl₂ → BaCl + Cl proceeds through different electronic channels with diametrically opposite collision dynamics: ground state BaCl(X²Σ) is formed via a direct interaction as witnessed by forward scattering and a strongly inverted internal state distribution. Electronically excited BaCl^*(C²Π) is formed via a long-lived collision complex, indicated by a statistical vibrational distribution. A simple RRK argument explains the differences of lifetimes towards unimolecular decomposition of the collision complexes. A lower limit of the BaCl(X²Σ⁺) dissociation energy is placed at 121 kcal/mole.     

Chemiluminescence of CaCl From the Ca+Cl2 Reaction in Argon Matrix

Visible chemiluminescence in the 5800-6600 Å region was observed from the Ca+Cl₂ reaction in an argon matrix. The longer wavelength doublet progression is assigned as the A²Π_{3/2, 1/2}→X²Σ⁺ transition of CaCl, with v₀₀= 16189 and 16126 cm^?1, respectively. Emission from the vibrationally excited v' = 1 level of the A state was also observed. This is the first observation of resolved spin-orbit components in matrix chemiluminescent reactions. The progression with v₀₀=16855 cm^?1 was assigned as the B²Σ⁺→X²Σ⁺ transition of CaCl. Both transitions showed very small matrix shifts in the T₂ values. A weak band at 17185 cm^?1 was assigned as either the E²Σ→B²Σ⁺ or the a⁴Σ⁺→A²Π transition of CaCl. Ca atomic emission at 4232 and 6574 Å was also observed and it was attributed to the energy transfer processes from excited CaCl radicals.     

Excited states of gaseous ions. Transitions to and predissociation of the CΣu state of n2

A configuration interaction study of different electronic states of N⁺₂ has been performed. The position in energy and the relative intensity of the photoelectron bands of the ²Σ⁺_u states has been calculated and compared with experiment. The C²Σ⁺_u state is predissociated by a ⁴Π_u state, as previously supposed. However, owing to the attractive nature of the ⁴Π_u state a double crossing occurs. Several predissociation mechanisms of the C state can therefore take place; their lifetimes have been calculated.