Molecules in high spin states III: the millimeter/submillimeter-wave spectrum of the MnCl radical (X (7)Sigma(+))

The pure rotational spectrum of the MnCl radical (X (7)Sigma(+)) has been recorded in the range 141-535 GHz using millimeter-submillimeter direct absorption spectroscopy. This work is the first time the molecule has been studied with rotational resolution in its ground electronic state. MnCl was synthesized by the reaction of manganese vapor, produced in a Broida-type oven, with Cl(2). Transitions of both chlorine isotopomers were measured, as well as lines originating in several vibrationally excited states. The presence of several spin components and manganese hyperfine interactions resulted in quite complex spectra, consisting of multiple blended features. Because 42 rotational transitions were measured for Mn(35)Cl over a wide range of frequencies with high signal-to-noise, a very accurate set of rotational, fine structure, and hyperfine constants could be determined with the aid of spectral simulations. Spectroscopic constants were also determined for Mn(37)Cl and several vibrationally excited states. The values of the spin-rotation and spin-spin parameters were found to be relatively small (gamma=11.2658 MHz and lambda=1113.10 MHz for Mn(35)Cl); in the case of lambda, excited electronic states contributing to the second-order spin-orbit interaction may be canceling each other. The Fermi contact hyperfine term was found to be large in manganese chloride with b(F)(Mn(35)Cl)=397.71 MHz, a result of the manganese 4s character mixing into the 12sigma orbital. This orbital is spsigma hybridized, and contains some Mn 4psigma character, as well. Hence, it also contributes to the dipolar constant c, which is small and positive for this radical (c=32.35 MHz for Mn(35)Cl). The hyperfine parameters in MnCl are similar to those of MnH and MnF, suggesting that the bonding in these three molecules is comparable.     

塞曼效应在Cl2+及其同位素分子离子光谱标识中的应用

The A2Πu-X2Πg electronic absorption spectrum of the Cl2+ molecular cation in the region between 16820 and 17350 cm-1 was observed by employing optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy. Cl2+ is a paramagnetic molecule; however, the intensities of some spectral lines, belonging to three bands whose origins are near 17282, 17324 and 16913 cm-1, respectively, remain unchanged with in the magnetic field. This indicates that both the upper and lower states have a weak Zeeman effect. The Zeeman contribution is nearly zero for the 2Π1/2 state, while nonvanishing for the 2Π3/2 state. Therefore, this behavior for the spectral assignment of Cl2+, including its isotopics was utilized and the identity of these bands was confirmed as members of the Ω=1/2 component of the electronic transition conveniently and unambiguously. The assigned bands are the (3, 7) band of the Ω=1/2 component of 35Cl+2 and 35Cl37Cl+ and the (2, 7) band of the Ω=1/2 component of 35Cl2+. It extends the range of vibrational assignments considerably in both the ground and the excited state, and leads to the successful rotational analysis. New molecular constants of Cl2+ were obtained from the observed line positions, band by band, using a weighted least squares fitting procedure.     

CCl2(A1B1)被O2及取代甲烷类分子猝灭的动力学研究

对CCl4／Ar混合气体放电产生CCl2自由基，再用541.52nm激光将电子基态CCl2激发到激发态A^1B1（0，4，0）振动态k=0能级上，通过检测 激发态CCl2时间分辨荧光信号，测得室温下CCl2(A^1B1)被O2，CF4，CF2Cl，CH3NO2，CH2Br2等分子猝灭的实验结果，用改进的三能级模型分析处理实验数据，获得态分辨速常数KA和Ka值，并对实验结果进行了讨论。     

Photofragment translational spectroscopy of ICl near 304 and 280 nm: Observation of an intense hot band effect

The photodissociation dynamics of ICl has been studied near 304 and 280 nm on a simple miniature time of flight (mini-TOF) photofragment translational spectrometer with a short pulse of a weak acceleration field. An intense hot band effect was observed. Many small peaks were resolved in each photofragment translational spectrum (PTS). Based on simulations, the principal peaks were assigned not only to the different photodissociation channels (1) I + Cl, (2) I + Cl*, (3) I* + Cl, or (4) I* + Cl*, but also to the different chlorine isotopes (35Cl and Cl). Moreover, some extra peaks showed the existence of an intense hot 37 band effect from vibrationally excited ICl molecules, though only a few percent of ICl molecules remained in the vibrationally excited states in our supersonic molecular beam. Based on the spectra near 304 nm, the quantum yield Ф of each channel, the curve crossing, and the branching fraction σ from each transition state were determined.     

High-energy collisional activation of the molecular ions of thiophene-2-one with different target gases

Collisional activation of keV thiophene-2-one radical cations 1(+*) with O(2) or NO(*) as the target gas leads to a desulfuration reaction. This peculiar reaction is insignificant or absent with other targets such as helium, argon, methane or nitrogen. The radical cations produced in this desulfuration reaction are most probably vinylketene ions, as indicated by a triple mass spectrometric (MS/MS/MS) experiment performed on a 'hybrid' tandem mass spectrometer of sector--quadrupole--sector configuration. Tentatively, it is proposed that population of an excited state accounts for the non-ergodic behavior of 1(+*) upon collision with oxygen or nitric oxide. Ab initio molecular orbital calculations using molecular orbital theory (UMP2, UCCSD(T)) and density functional theory (B3LYP) with 6--31G(d,p) and 6--311++G(d,p) basis sets were used to evaluate the relative energy of the excited quartet state of 1(+*) radical cations. This quartet state is calculated to lie about 3.6 eV above the (2)A(") ground state and 0.9 eV above the C(4)H(4)O(+*)+S dissociation products. It is proposed that the quartet ion serves as the precursor for the spontaneous desulfuration.     

First-row transition-metal chloride complexes of the wide bite-angle diphosphine (iPr)DPDBFphos and reactivity studies of monovalent nickel

The diphosphine 4,6-bis(3-diisopropylphosphinophenyl)dibenzofuran (abbreviated as (iPr)DPDBFphos) has been metalated with transition metal dichlorides of zinc, cobalt, and nickel to yield ((iPr)DPDBFphos)MCl(2) complexes. Within these compounds, the diphosphine (iPr)DPDBFphos adapts a wide range of bite angles (115 to 180°) as determined by X-ray crystallography. A three-coordinate planar Ni(I) species was isolated from the reduction of ((iPr)DPDBFphos)NiCl(2) with KC(8). Low-temperature electron paramagnetic resonance (EPR) measurements of ((iPr)DPDBFphos)NiCl allow the determination of g values (2.09, 2.14, 2.37) and hyperfine coupling constants to two (31)P nuclei, A(iso) = 46 × 10(-4) cm(-1), and one (37)Cl/(35)Cl nucleus, A = (12, 0.7, 35) × 10(-4) cm(-1). Density functional theory (DFT) studies reveal the nature of the magnetic orbital to be d(xy), which has σ-antibonding and π(∥)-antibonding interactions with the phosphorus and chloride atoms, respectively. The monovalent nickel complex reacts with substrates containing C-X bonds; and in the case of vinyl chloride, a Ni(II) vinyl species ((iPr)DPDBFphos)Ni(CH═CH(2))Cl is generated along with the Ni(II) dichloride complex. The monovalent Ni(I) chloride is an active catalyst in the Kumada cross-coupling reaction of vinyl chloride and phenyl Grignard reagent.     

A crossed molecular beam imaging study of the O(1D2)+HCl-->OH+Cl(2P J=3/2, 1/2) reaction.

A crossed molecular beam study is presented for the O((1)D(2))+HCl-->OH+Cl((2)P(J)) reaction at the collision energy of 6 kcal mol(-1). State-resolved doubly differential cross sections are obtained for the Cl((2)P(J=3/2) ) and Cl*((2)P(J=1/2) ) products by velocity-map ion imaging. Both products are slightly more forward scattered, which suggests a reaction mechanism without a long-lived intermediate in the ground electronic state. A small fraction (23 %) of the energy release into the translational degree of freedom indicates strong internal excitation of the counterpart OH radical. The contribution of the electronic excited states of O--HCl to the overall reaction is also examined from the doubly differential cross sections.     

On the spin-orbit splitting of CuCl2 in its 2 Pi g ground state

The spin-orbit splitting of CuCl(2) in its ground X(2)Pi(g) state remains an unknown or, at best, poorly defined quantity. The electronic spectrum of CuCl(2) has been studied by Fourier transform resolved, laser-induced fluorescence between 602 and 587 nm, in an attempt to identify transitions to the upper spin component of the ground state. In order to provide a well-defined excitation process, the sample was cooled to rotational temperatures of about 10 K in a free-jet expansion. Observations from just two rotationally perturbed levels in the upper electronic state, one for (63)Cu(35)Cl(2) and the other for (65)Cu(35)Cl(37)Cl, have revealed an additional feature about 482 cm(-1) above the (2)Pi(3/2) state. The effective rotational constants associated with these levels (0.066 20 cm(-1) for (63)Cu(35)Cl(2)) are significantly larger than those for the ground (2)Pi(3/2) state (0.058 13 cm(-1)). Analysis of this feature as the (2)Pi(1/2) component leads to a value of -482.9 cm(-1) for the spin-orbit coupling constant A and of -0.0846 cm(-1) for the lambda-doubling parameter (p+2q) for (63)Cu(35)Cl(2). Several other previously unobserved levels are also identified within 2000 cm(-1) of the ground state. Many of these also have anomalously large rotational constants.     

Rotational spectra of 1-chloro-2-fluoroethylene. I. Main isotopologues and deuterated species of the trans isomer

Guided by theoretical predictions, the rotational spectra of the mono- and bideuterated species of trans-1-chloro-2-fluoroethylene, CH35Cl=CDF, CH37Cl=CDF, CD35Cl=CHF, CD37Cl=CHF, CD35Cl=CDF, and CD37Cl=CDF, have been recorded for the first time. Assignment of the Delta J = 0 and Delta K(-1) = +1 bands with K(-1) = 3,4,5,... (all isotopic species) as well as of several Delta J = +/-1 and Delta K(-1) = +1 transitions (all isotopic species except CH37Cl=CDF, CD37Cl=CHF, and CD37Cl=CDF) led to the accurate determination of the ground-state rotational constants, the quartic, and some sextic centrifugal distortion constants, as well as the nuclear quadrupole coupling constants for both 35Cl and 37Cl in good agreement with corresponding theoretical predictions based on high-level coupled-cluster calculations. Inconsistencies of the present spectroscopic parameters with respect to those reported earlier for the two main isotopologues, i.e., CH35Cl=CHF and CH37Cl=CHF, necessitated a reinvestigation of the rotational spectra for these two isotopic species. Supported by quantum chemical calculations, the previously recorded spectra are reassigned to a vibrationally excited state, while analysis of the Delta J = 0 and Delta K(-1) = +1 as well as some Delta J = +/-1 and Delta K(-1) = +1 transitions provided a revised set of spectroscopic parameters for the vibrational ground state of these two isotopic species.     

Ab initio study on the decomposition of first excited state HOOO radicals

The HOOO radical plays a crucial role in atmospheric processes involving the OH radical and O(2) molecule. We present an ab initio molecular orbital theory study on the decomposition reaction of the first excited state HOOO((2)A') with respect to OH and O(2). The geometries and harmonic vibrational frequencies of all stationary points are calculated at the CASSCF and MRCI levels of theory in conjunction with the 6-31+G(d,p) basis set. The potential energy profile of the decomposition reaction is studied at the CASSCF/6-31+G(d,p) level of theory, in which the complete valence orbitals and electrons are included in the active space. The energies of the potential energy profile are further refined at the CASPT2 and MRCI levels of the theory. Additionally, we have determined the interesting reaction process: the HOOO((2)A') radical with C(s) symmetry does not dissociate to OH((2)Pi) and O(2)((3)Sigma(-)(g)) directly as this is forbidden by orbital symmetry, but dissociates to OH((2)Pi) and O(2)((3)Sigma(-)(g)) via the change in symmetry from C(s) to C(infinity v) symmetry with a low barrier.     

Perturbations in the pure rotational spectrum of CoCl (X 3 Phi i): a submillimeter study

The millimeter/submillimeter-wave spectrum of the CoCl radical (X (3)Phi(i)) has been recorded using direct absorption techniques in the frequency range 340-510 GHz. This work is the first pure rotational study of this molecule. The radical was created by the reaction of Cl(2) with cobalt vapor. Rotational transitions arising from the Omega=4, 3, and 2 spin-orbit components of Co(35)Cl have been measured, all of which exhibit hyperfine splittings due to the (59)Co nucleus (I=7/2). Transitions arising from the Co(37)Cl species were also recorded, as well as those originating in the v=1, 2, 3, and 4 vibrational states of both isotopomers. The spin-orbit pattern exhibited by the molecule is unusual, with the Omega=3 component significantly shifted relative to the other spin components. In addition, the regular octet hyperfine splittings become distorted above a certain J value for the Omega=3 transitions only. These effects suggest that the molecule is highly perturbed in its ground state, most likely a result of second-order spin-orbit mixing with a nearby isoconfigurational (1)Phi(3) state. The complete data set for Co(35)Cl and Co(37)Cl were fit successfully with a case (a) Hamiltonian but required a large negative spin-spin constant of lambda=-7196 GHz and higher order centrifugal distortion corrections to the rotational, spin-orbit, spin-spin, and hyperfine terms. The value of the spin-spin constant suggests that the Omega=3 component is shifted to higher energy and lies near the Omega=2 sublevel. The hyperfine parameters are consistent with a delta(3)pi(3) electron configuration and indicate that CoCl is more covalent than CoF.     

CCl2自由基被无机小分子猝灭的速率常数

对CCl4/Ar混合气体脉冲直流高压放电产生CCl2自由基,用541.52 nm激光将电子基态CCl2激励到A 1B1(0,4,0)振动能级上. 通过检测激发态CCl2时间分辨荧光信号,测得室温下CCl2(A 1B1和a 3B1)被O2、N2、NO、 CO2、 CS2、H2O、SO2,和SF6分子猝灭的实验结果.用我们提出的三能级模型分析处理实验数据,获得了CCl2(A 1B1)态和CCl2(a 3B1)态的碰撞猝灭速率常数kA和ka值.     

Hot bands in jet-cooled and ambient temperature spectra of chloromethylene

Rotationally resolved spectra of several bands lying to the red of the origin of the A(1)A" - X (1)A' band system of chloromethylene (HCCl), were recorded by laser absorption spectroscopy in ambient temperature and jet-cooled samples. The radical was made by excimer laser photolysis of dibromochloromethane, diluted in inert gas, at 193 nm. The jet-cooled sample showed efficient rotational but less vibrational cooling. Analysis showed that the observed bands originate in the (upsilon(1),upsilon(2),upsilon(3)) = (010), (001), and (011) vibrational levels of the ground electronic state of the radical, while the upper-state levels involved were (000), (010), (001), and (011). Vibrational energies and rotational constants describing the rotational levels in the lower-state vibrational levels were determined by fitting to combination differences. The analysis also resulted in a reevaluation of the C-Cl stretching frequency in the excited state and we find E(001)' = 13 206.57 or 926.17 cm(-1) above the A(1)A" (000) rotationless level for HC(35)Cl. Scaled ab initio potential energy surfaces for the A and X states were used to compute the transition moment surface and thereby the relative intensities of different vibronic transitions, providing additional support for the assignments and permitting the prediction of the shorter wavelength spectrum. All the observed upper state levels showed some degree of perturbation in their rotational energy levels, particularly in K(a) = 1, presumably due to coupling with near-resonant vibrationally excited levels of the ground electronic state. Transitions originating in the low-lying a(3)A" were also predicted to occur in the same wavelength region, but could not be identified in the spectra.     

CCl2(A 1B 1,a3B1)自由基被烷烃类分子猝灭动力学

用放电 LIF实验装置,对CCl4/Ar混合气体放电产生CCl2自由基,再用541.52 nm激光将电子基态CCl2激励到激发态A 1B1(0,4,0)振动能级上,通过检测激发态CCl2时间分辨荧光信号,测得室温下CCl2(A 1B1)被烷烃类分子猝灭的实验结果,用我们提出的三能级模型分析处理实验数据,获得CCl2(A 1B1)态和CCl2(a 3B1)态的碰撞猝灭速率常数kA和ka值.     

A stable dialkylphosphinyl radical

Dialkylphosphinyl radical 1 was synthesized as thermally stable yellow crystals and found to be monomeric both in solution and in the solid state. EPR spectrum showed that the spin density of 1 is mainly localized on the 3p orbital of the dicoordinated phosphorus atom. A distinct absorption band due to the electronic transition from nonbonding electron pair orbital to singly occupied 3p orbital on the phosphorus atom of 1 was observed at 445 nm in solution. Phosphinyl radical 1 underwent facile reaction with carbon tetrachloride, hydrogen abstraction, and a unique reaction with a persistent radical, galvinoxyl, giving a cyclic phosphaalkene and a silylether.     

Photodissociation of the BrO radical using velocity map ion imaging: excited state dynamics and accurate D0(0)(BrO) evaluation

We have studied the photodissociation dynamics of expansion-cooled BrO radical both above (278-281.5 nm) and below (355 nm) the A (2)Pi(3/2) state threshold using velocity map ion imaging. A recently developed late-mixing flash pyrolytic reactor source was utilized to generate an intense BrO radical molecular beam. The relative electronic product branching ratios at 355 nm and from 278 to 281.5 nm were determined. We have investigated the excited state dynamics based on both the product branching and the photofragment angular distributions. We find that above the O((1)D(2)) threshold the contribution of the direct excitation to states other than the A (2)Pi(3/2) state and the role of curve crossing is considerably larger in BrO compared to that observed for ClO, in agreement with recent theoretical studies. The measurement of low velocity photofragments resulting from photodissociation just above the O((1)D(2)) threshold provides an accurate and direct determination of the A (2)Pi(3/2) state dissociation threshold of 35418+/-35 cm(-1), leading to a ground state bond energy of D(0)(0)(BrO)=55.9+/-0.1 kcal/mol.     

Excited state dynamics of a PtII diimine complex bearing a naphthalene-diimide electron acceptor

A combination of picosecond time-resolved infrared spectroscopy, picosecond transient absorption spectroscopy, and nanosecond flash photolysis was used to elucidate the nature and dynamics of a manifold of the lowest excited states in Pt(phen-NDI)Cl 2 ( 1), where NDI = strongly electron accepting 1,4,5,8-naphthalene-diimide group. 1 is the first example of a Pt (II)-diimine-diimide dyad. UV/vis/IR spectroelectrochemistry and EPR studies of electrochemically generated anions confirmed that the lowest unoccupied molecular orbital (LUMO) in this system is localized on the NDI acceptor group. The lowest allowed electronic transition in Pt(phen-NDI)Cl 2 is charge-transfer-to-diimine of a largely Pt-->phen metal-to-ligand charge-transfer (MLCT) character. Excitation of 1 in the 355-395 nm range initiates a series of processes which involve excited states with the lifetimes of 0.9 ps ( (1)NDI*), 3 ps ( (3)MLCT), 19 ps (vibrational cooling of "hot" (3)NDI and of "hot" NDI ground state), and 520 mus ( (3)NDI). Excitation of 1 with 395 nm femtosecond laser pulses populates independently the (1)MLCT and the (1)NDI* excited states. A thermodynamically possible decay of the initially populated (1)MLCT to the charge-transfer-to-NDI excited state, [Pt (III)(phen-NDI (-*))Cl 2], is not observed. This finding could be explained by an ultrafast ISC of the (1)MLCT to the (3)MLCT state which lies about 0.4 eV lower in energy than [Pt (III)(phen-NDI (-*))Cl 2]. The predominant decay pathway of the (3)MLCT is a back electron transfer process with approximately 3 ps lifetime, which also causes partial population of the vibrationally hot ground state of the NDI fragment. The decay of the (1)NDI* state in 1 populates vibrationally hot ground state of the NDI, as well as vibrationally hot (3)NDI. The latter relaxes to form (3)NDI state, that is, [Pt(phen- (3)NDI)Cl 2]*, which possesses a remarkably long lifetime for a Pt (II) complex in fluid solution of 520 mus. The IR signature of this excited state includes the nu(CO) bands at 1607 and 1647 cm (-1), which are shifted considerably to lower energies if compared to their ground-state counterparts. The assignment of the vibrational bands is supported by the density-functional theory calculations in CH 2Cl 2. Pt(phen-NDI)Cl 2 acts as a modest photosensitizer of singlet oxygen.     

The dissociation dynamics of He...I 35Cl(B,v'=2,3) complexes with varying amounts of internal energy

The He...I (35)Cl intermolecular vibrational levels with n'=0-6 that are bound within the He+ICl(B,v'=3) potential [A. B. McCoy, J. P. Darr, D. S. Boucher, P. R. Winter, M. D. Bradke, and R. A. Loomis, J. Chem. Phys. 120, 2677 (2004)] are identified in laser-induced fluorescence experiments performed at very low temperatures within a supersonic expansion. Comparisons of the positions and intensities of these lines with the excitation spectra, calculated using potential surfaces to describe the interactions between the helium atom and ICl in its ground and excited state, assist in the assignments. Based on these comparisons the excited state potential was rescaled so that the experimental and calculated J'=0 energies agree to within the experimental uncertainties for all but the lowest, n'=0, intermolecular level. Two-laser, action, and pump-probe spectroscopy experiments indicate that the bound He...I (35)Cl(B,v'=3) intermolecular vibrational levels undergo vibrational predissociation forming rotationally excited I (35)Cl(B,v'=2,j') products with distributions that depend upon the initial intermolecular vibrational level excited. Action spectra recorded in the ICl B-X, 2-0 region while monitoring the Deltav=0, I (35)Cl(B,v'=2) channel reveal two additional dissociation mechanisms for the He...I (35)Cl(B,v') excited state complexes: rotational predissociation of discrete metastable states lying slightly above the He+I (35)Cl(B,v'=2) asymptote and direct dissociation that occurs when the linear conformer is excited to the continuum of states above the same asymptote. The rotational predissociation pathway forms I (35)Cl(B,v'=2,j') products in all of the rotational states energetically accessible. The direct dissociation mechanism yields very cold rotational product state distributions; for instance, the average rotational energy in the product state distribution measured when the linear complexes are prepared 20 cm(-1) above the dissociation limit is only 1.51 cm(-1), representing only 7.6% of the available energy.     

High-resolution spectroscopy on the B2Σ+,ν' = 0→X2Π, ν″ =1 transition in SiCl

High-resolution laser-induced fluorescence spectra of²⁸Si³⁵Cl and ²⁸Si³⁷Cl have been observed in a molecular beam. Accurate constants describing the rotational structure in the X ²Π, ν″ = 1 as well as in the electronically excited B ²Σ⁺, ν' = 0 state are given. An inverted fine structure was found in the excited state with a spin-splitting constant γ = −31.15±0.19 MHz for Si³⁵Cl and γ = −30.62 ±0.61 MHz for Si³⁷Cl.     

The hydrogen-bonded 2-pyridone dimer model system. 2. Femtosecond mid-infrared pump-probe study

2-Pyridone (PD) tautomerises to 2-hydroxypyridine (HP) in liquid solution, the equilibrium of which is solvent dependent. Dimerization of PD and HP leads to the cyclic dimers (PD)(2), (HP)(2), and (PD-HP). A combined NMR and FT-IR study [Szyc, ?.; et al. J. Phys. Chem. A 2010, 114, 7749-7760] has shown that solutions of 2-pyridone in CD(2)Cl(2) constitute mainly PD-CD(2)Cl(2) solute-solvent complexes and cyclic dimers (PD)(2). Because of a lack of specific marker modes, a contribution of the cyclic dimer (HP)(2) to the NH/OH stretching absorption between 2400 and 3300 cm(-1) could not be fully ruled out. Here, we present the first ultrafast infrared (IR) pump-probe experiments on the NH/OH stretching region of a solution of 2-pyridone in CD(2)Cl(2). The temporally and spectrally resolved data reveal different rate-like relaxation processes with time constants between 150 fs and 20 ps as well as coherent low-frequency oscillations due to hydrogen bond modes. An analysis shows that the transient behavior is dominated by a single hydrogen bonded species. We compare the low-frequency wavepacket motions, observed with 99 and 150 cm(-1) frequencies, with literature values as well as our quantum chemical calculations and conclude that this single molecular species is cyclic (PD)(2).