CH2BrCl在265 nm光解产生的氯甲基自由基的振动内能

利用离子速度影像技术研究了CH2BrCl在265nm附近的激光光解.利用2+1共振增强多光子电离分别获得光解产物Br(2P1/2)和Br(2P3/2)的离子速度图像,从而得出Br(2P1/2)和Br(2P3/2)的速度分布,以及光解碎片的总平动能分布.据此,运用角动量守恒碰撞模型获得了解离氯甲基自由基(·CH2Cl)的振动内能分布.研究结果表明:CH2BrCl+hv→Br(2P1/2)+CH2Cl通道产生的氯甲基自由基中被激发的振动模主要是v4、v3+v4、v2+v4和v2+v6;CH2BrCl+hv→Br(2P3/2)+CH2Cl通道产生的氯甲基自由基中被激发的振动模主要是v2+v6、v1+v3、v2+v5、v2+v3+v5和v1+v5;母体分子CH2BrCl在吸收光解光子后除有v5(CBrstretch)振动模被激发外,还有v7(CH2a-stretch)等其它振动模也被激发.     

A 193 nm laser photofragmentation time-of-flight mass spectrometric study of chloroiodomethane

The photodissociation dynamics of chloroiodomethane (CH2ICl) at 193 nm has been investigated by employing the photofragment time-of-flight (TOF) mass spectrometric method. Using tunable vacuum ultraviolet undulator synchrotron radiation for photoionization sampling of nascent photofragments, we have identified four primary dissociation product channels: CH2Cl + I(2P(1/2))/I(2P(3/2)), CH2I + Cl(2P(1/2))/Cl(2P(3/2)), CHI + HCl, and CH2 + ICl. The state-selective detection of I(2P(3/2)) and I(2P(1/2)) has allowed the estimation of the branching ratio for I(2P(1/2)):I(2P(3/2)) to be 0.73:0.27. Theoretical calculations based on the time-dependent density-functional theory have been also made to investigate excited electronic potential-energy surfaces, plausible intermediates, and transition structures involved in these photodissociation reactions. The translation energy distributions derived from the TOF measurements suggest that at least two dissociation mechanisms are operative for these photodissociation processes. One involves the direct dissociation from the 2 1A' state initially formed by 193 nm excitation, leading to significant kinetic-energy releases. For the I-atom and Cl-atom elimination channels, the fragment kinetic-energy releases observed via this direct dissociation mechanism are consistent with those predicted by the impulsive dissociation models. Other mechanisms are likely predissociative or statistical in nature from the lower 1 1A' and 1 1A' states and/or the ground X 1A' state populated by internal conversion from the 2 1A' state. On the basis of the maximum kinetic-energy release for the formation of CH2Cl + I(2P(1/2)), we have obtained a value of 53+/-2 kcal/mol for the 0 K bond dissociation energy of I-CH2Cl. The intermediates and transition structures for the CHI + HCl and CH2 + ICl product channels have been also investigated by ab initio quantum calculations at the MP2(full)/6-311G(d) and B3LYP(full)/6-11G(d) levels of theory. The maximum kinetic-energy releases observed for the CHI + HCl and CH2 + ICl channels are consistent with the interpretation that the formation of CHI and CH2 in their ground triplet states is not favored.     

Combined vacuum ultraviolet laser and synchrotron pulsed field ionization study of CH2BrCl

The pulsed field ionization-photoelectron (PFI-PE) spectrum of bromochloromethane (CH2BrCl) in the region of 85,320-88,200 cm-1 has been measured using vacuum ultraviolet laser. The vibrational structure resolved in the PFI-PE spectrum was assigned based on ab initio quantum chemical calculations and Franck-Condon factor predictions. At energies 0-1400 cm-1 above the adiabatic ionization energy (IE) of CH2BrCl, the Br-C-Cl bending vibration progression (nu1+=0-8) of CH2BrCl+ is well resolved and constitutes the major structure in the PFI-PE spectrum, whereas the spectrum at energies 1400-2600 cm-1 above the IE(CH2BrCl) is found to exhibit complex vibrational features, suggesting perturbation by the low lying excited CH2BrCl+(A 2A") state. The assignment of the PFI-PE vibrational bands gives the IE(CH2BrCl)=85,612.4+/-2.0 cm-1 (10.6146+/-0.0003 eV) and the bending frequencies nu1+(a1')=209.7+/-2.0 cm-1 for CH2BrCl+(X2A'). We have also examined the dissociative photoionization process, CH2BrCl+hnu-->CH2Cl++Br+e-, in the energy range of 11.36-11.57 eV using the synchrotron based PFI-PE-photoion coincidence method, yielding the 0 K threshold or appearance energy AE(CH2Cl+)=11.509+/-0.002 eV. Combining the 0 K AE(CH2Cl+) and IE(CH2BrCl) values obtained in this study, together with the known IE(CH2Cl), we have determined the 0 K bond dissociation energies (D0) for CH2Cl+-Br (0.894+/-0.002 eV) and CH2Cl-Br (2.76+/-0.01 eV). We have also performed CCSD(T, full)/complete basis set (CBS) calculations with high-level corrections for the predictions of the IE(CH2BrCl), AE(CH2Cl+), IE(CH2Cl), D0(CH2Cl+-Br), and D0(CH2Cl-Br). The comparison between the theoretical predictions and experimental determinations indicates that the CCSD(T, full)/CBS calculations with high-level corrections are highly reliable with estimated error limits of <17 meV.     

The dynamics of Br(2Pj) formation in the photodissociation of vinyl and perfluorovinyl bromides

The photodissociation dynamics of vinyl bromide and perfluorovinyl bromide have been investigated at 234 nm using a photofragment ion imaging technique coupled with a state-selective [2+1] resonance-enhanced multiphoton ionization scheme. The nascent Br atoms stem from the primary C-Br bond dissociation leading to the formation of C2H3(X) and Br(2Pj;j=1/2,3/2). The obtained translational energy distributions have been well fitted by a single Boltzmann and three Gaussian functions. Boltzmann component has not been observed in the perfluorovinyl bromide. The repulsive 3A'(n,sigma *) state has been considered as the origin of the highest Gaussian components. Middle translational energy components with Gaussian shapes are produced from the 1A"(pi,sigma*) and/or 3A"(pi,sigma*) which are very close in energy. Low-energy Gaussian components are produced via predissociation from the 3A'(pi,pi*) state. The assignments have also been supported by the recoil anisotropy corresponding to the individual components. It is suggested that intersystem crossing from the triplet states to the ground state has been attributed to the Boltzmann component and the fluorination reduces the probability of this electronic relaxation process.     

A theoretical investigation of the feasibility of Tannor-Rice type control: application to selective bond breakage in gas-phase dihalomethanes

Within the B? absorption band of CH(2)BrCl, we theoretically analyze the laser-induced control of the Br/Cl branching ratio, Br + CH(2)Cl ← CH(2)BrCl → CH(2)Br + Cl, with CH(2)BrCl initially in its vibrational ground state. For weak-field excitation, the Br/Cl branching ratio increases as a function of wavelength, however, for wavelengths below 180 nm the branching ratio cannot be made smaller than 0.4. Using optimal control theory, we show that the branching ratio can be made significantly less than 0.4, only when very strong fields are employed. Thus, the present work strongly suggests that a Tannor-Rice type laser control mechanism for selective bond breakage in CH(2)BrCl cannot take place without accompanying photoionization.     

Photodissociation dynamics of CBr4 at 267 nm by means of ion velocity imaging

The photodissociation dynamics of CBr4 at 267 nm has been studied using time of flight (TOF) mass spectrometry and ion velocity imaging techniques. The photochemical products are detected with resonance enhanced multiphoton ionization (REMPI) as well as single-photon vacuum ultraviolet ionization at 118 nm. REMPI at 266.65 and 266.71 nm was used to detect the ground Br(2P32) and spin-orbit excited Br(2P12) atoms, respectively. The translational energy and angular distributions are consistent with direct dissociation from an excited triplet state and indirect dissociation from high vibrational levels on the singlet ground state surface. Br2+ ions are also observed in the TOF spectra with a focused 267 nm laser. The counter fragment, CBr2+, is observed when this photolysis laser is unfocused, and photons at 118 nm are used to ionize the radical products. The translational energy distributions of the CBr2+ and Br2+ products can be momentum matched, which indicates that molecular Br2 elimination is one of the primary dissociation channels.     

A concerted three-body formation X+Y+C2H4 in the photodissociation of CH2XCH2Y (X,Y=Br,Cl) at 193 nm

The photodissociation of CH2XCH2Y (X,Y=Br,Cl) through absorption of 193 nm photons was investigated using product translational spectroscopy. No stable CH2BrCH2 or CH2ClCH2 was detected. The recorded time-of-flight spectra indicate that these internally excited radicals dissociated into Y+C2H4 in a concerted reaction with the first C-X bond rupture. Product anisotropy implies that the overall reaction time for three-body formation is in a fraction of rotational period. According to an asynchronous concerted reaction model, the measured spectra were simulated with product translational energy distributions coupled by asymmetric angular distributions. For the mixed halide, CH2BrCH2Cl, triple products Br+Cl+C2H4 can be originated from the cleavage of either the C-Br bond or the C-Cl bond. The results are discussed and where appropriate, comparisons with previous investigations of the related molecules are included.     

离子速度成像方法研究二溴甲烷的紫外光解动力学

利用二维离子速度成像(Ion-Velocity Imaging)方法对二溴甲烷分子在234和267 nm附近的光解动力学行为进行了研究. 实验中得到了二溴甲烷光解产生的Br^*(²P_1/2)和Br(²P_3/2)在不同波长下的角度和平动能分布. 在平动能分布中发现两个高斯分布, 推测其中主要是C—Br的快速解离, 而高能宽分布则来自于CH₂Br自由基的二次解离过程. 通过角度分布得到了Br^*与Br中来自直接解离和非绝热交叉跃迁两种来源的比例. 结果表明Br^*原子主要来自于B₁态的直接解离, 而Br则绝大部分是从B₁态向A₁的非绝热交叉跃迁得到, 并导致了两种解离通道能量分布的差别.     

A two-dimensional wavepacket study of the nonadiabatic dynamics of CH2BrCl

The nonadiabatic photodissociation dynamics of CH2BrCl into CH2Br + Cl or CH2Cl + Br is studied using two-dimensional wavepacket propagations on ab initio multiconfigurational MS-CASPT2 potential energy surfaces. Using a three-state diabatic model, we investigate the electronic states responsible for the two competing fragmentation channels and how the conical intersection present between the two lowest excited states affects the dissociation rate. Within this model, we find that the Br/Cl branching ratio depends on the irradiation wavelength. Predominant C-Br fragmentation occurs for wavelengths longer than 200 nm, while nonadiabatic C-Cl dissociation with a constant branching ratio of 0.4 is predicted upon absorption of photons in the range of 170-180 nm. Additionally, we observe complete nonadiabatic population transfer in less than 100 fs, that is, before the wavepacket can reach the conical intersection. As a consequence, there is no three-body CH2 + Br + Cl dissociation.     

Coherent control of the ultrafast dissociative ionization dynamics of bromochloroalkanes

We report on the coherent control of the ultrafast ionization and fragmentation dynamics of the bromochloroalkanes C(2)H(4)BrCl and C(3)H(6)BrCl using shaped femtosecond laser pulses. In closed-loop control experiments on bromochloropropane (C(3)H(6)BrCl) the fragment ion yields of CH(2)Cl(+), CH(2)Br(+), and C(3)H(3)(+) are optimized with respect to that of the parent cation C(3)H(6)BrCl(+). The fragment ion yields are recorded in additional experiments in order to reveal the energetics of cation fragmentation, where laser-produced plasma radiation is used as a tunable pulsed nanosecond vacuum ultraviolet radiation source along with photoionization mass spectrometry. The time structure of the optimized femtosecond laser pulses leads to a depletion of the parent ion and an enhancement of the fragment ions, where a characteristic sequence of pulses is required. Specifically, an intense pump pulse is followed by a less intense probe pulse where the delay is 0.5 ps. Similarly optimized pulse shapes are obtained from closed-loop control experiments on bromochloroethane (C(2)H(4)BrCl), where the fragment ion yield of CH(2)Br(+) is optimized with respect to that of C(2)H(4)BrCl(+) as well as the fragment ion ratios C(2)H(2)(+)/CH(2)Br(+) and C(2)H(3)(+)/C(2)H(4)Cl(+). The assignment of the underlying control mechanism is derived from one-color 804 nm pump-probe experiments, where the yields of the parent cation and several fragments show broad dynamic resonances with a maximum at Δt = 0.5 ps. The experimental findings are rationalized in terms of dynamic ionic resonances leading to an enhanced dissociation of the parent cation and some primary fragment ions.     

Br(2Pj) atom formation dynamics in ultraviolet photodissociation of tert-butyl bromide and iso-butyl bromide

The photodissociation dynamics of tert-C(4)H(9)Br and iso-C(4)H(9)Br has been studied at 234 and 265 nm using two-dimensional velocity map imaging technique. The translational energy and angular distributions have been analyzed for Br, Br(*), and tert-C(4)H(9) radical. The energy distribution of Br atom in the photodissociation of tert-C(4)H(9)Br is found to consist of two Gaussian components. The two components are correlated to two independent reaction paths on the excited potential energy surfaces: (1) the high-energy component from the prompt dissociation along the C-Br stretching mode and (2) the low-energy component from the repulsive mode along the C-Br stretching, coupled with some bending motions. For the energy distribution of Br(*) atom in the photodissociation of tert-C(4)H(9)Br, a third multiphoton dissociative ionization channel is observed at 265 nm in addition to the two energy components corresponding to channels (1) and (2). The energy distributions of Br and Br(*) atoms in the photodissociation of iso-C(4)H(9)Br can be fitted using only one Gaussian function indicating a single formation channel. Relative quantum yields for Br((2)P(32)) at 234 and 265 nm in the photodissociation of tert-C(4)H(9)Br are measured to be 0.76 and 0.65, respectively. For iso-C(4)H(9)Br, the measured value is Phi(234 nm)(Br)=0.81. The contribution of bending modes to Br and Br(*) is much more obvious in the photodissociation of tert-C(4)H(9)Br than in iso-C(4)H(9)Br.     

Photodissociation dynamics of CH(2)Br(2) near 234 and 267 nm

The photodissociation dynamics of CH(2)Br(2) was investigated near 234 and 267 nm. A two-dimensional photofragment ion velocity imaging technique coupled with a [2+1] resonance-enhanced multiphoton (REMPI) ionization scheme was utilized to obtain the angular and translational energy distributions of the nascent Br ((2)P(3/2)) and Br* ((2)P(1/2)) atoms. The obtained translational energy distributions of Br and Br* are found consist of two components which should be come from the radical channel and secondary dissociation process, respectively. It is suggested that the symmetry reduction from C(2v) to C(s) during photodissociation invokes a non-adiabatic coupling between the 2B(1) and A(1) states. Consequently, the higher internal energy distribution of Br channel than Br* formation channel and the broader translational energy distribution of the former are presumed correlate with a variety of vibrational excitation disposal at the crossing point resulting from the larger non-adiabatic crossing from 2B(1) to A(1) state than the reverse crossing. Moreover, the measured anisotropy parameter beta indicate that fragments recoil along the Br-Br direction mostly in the photodissociation.     

Photodissociation dynamics of the ethoxy radical investigated by photofragment coincidence imaging

The photodissociation dynamics of the ethoxy radical (CH3CH2O) have been studied at energies from 5.17 to 5.96 eV using photofragment coincidence imaging. The upper state of the electronic transition excited at these energies is assigned to the C2A'state on the basis of electronic structure calculations. Fragment mass distributions show two photodissociation channels, OH + C2H4 and CH3 + CH2O. The presence of an additional photodissociation channel, identified as D + C2D4O, is revealed in time-of-flight distributions from the photodissociation of CD3CD2O. The product branching ratios and fragment translational energy distributions for all of the observed mass channels are nonstatistical. Moreover, the significant yield of OH + C2H4 product suggests that the mechanism for this channel involves isomerization on the excited-state surface. Photodissociation at a much lower yield is seen following excitation at 3.91 eV, corresponding to a vibronic band of the B2A' <-- X2A' transition.     

Bromine-loss and hydrogen-loss dissociations in low-lying electronic states of the CH3Br+ ion studied using multiconfiguration second-order perturbation theory

Complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) calculations with an ANO-RCC basis were performed for the 1(2)A', 1(2)A", 2(2)A', and 2(2)A" states of the CH3Br+ ion. The 1(2)A' state is predicted to be the ground state. The 2(2)A' state is predicted to be a bound state. The adiabatic and vertical excitation energies and the relative energies at the molecular geometry were calculated, and the energetic results for 2(2)A' and 2(2)A" are in reasonable agreement with the experimental data. Potential energy curves (PECs) for Br-loss and H-loss dissociations from the four C(s) states were calculated at the CASPT2//CASSCF level and the electronic states of the CH3(+) and CH2Br(+) ions as the dissociation products were determined by checking the relative energies and geometries of the asymptote products along the PECs. In the Br-loss dissociation, the 1(2)A', 1(2)A", and 2(2)A' states correlate with CH3(+) (X1A1') and the 2(2)A" state correlates with CH3(+) (1(3)A"). The energy increases monotonically with the R(C-Br) value along the four Br-loss PECs. In the H-loss dissociation the 1(2)A', 1(2)A", 2(2)A', and 2(2)A" states correlate with the X(1)A(1), 1(3)A", 1(3)A', and 1(1)A" states (1(3)A' lying above 1(1)A") of CH2Br(+), respectively. Along the 2(2)A" H-loss PEC there is an energy barrier and the CASSCF wave functions at large R(C-H) values have shake-up ionization character. Along the 2(2)A' H-loss PEC there are an energy barrier and a minimum. At the end of the present paper we present a comprehensive review on the electronic states and the X-loss and H-loss dissociations of the CH(3)X(+) (X = F, Cl, and Br) ions on the basis of our previous studies and the present study.     

Multiphoton dissociation dynamics of BrCl and the BrCl+ cation

Ion imaging methods have enabled identification of three mechanisms by which (79)Br(+) and (35)Cl(+) fragment ions are formed following one-color multiphoton excitation of BrCl molecules in the wavelength range 324.6 > lambda > 311.7 nm. Two-photon excitation within this range populates selected vibrational levels (v'= 0-5) of the [X (2)Pi(1/2)]5ssigma Rydberg state. Absorption of a third photon results in branching between (i) photoionization (i.e. removal of the Rydberg electron-a traditional 2 + 1 REMPI process) and (ii)pi*<--pi excitation within the core, resulting in formation of one or more super-excited states with Omega= 1 and configuration [A (2)Pi(1/2)]5ssigma. The fate of the latter states involves a further branching. They can autoionize (yielding BrCl(+)(X (2)Pi) ions in a wider range of v(+) states than formed by direct 2 + 1 REMPI). Further, one-photon absorption by the parent ions resulting from direct ionization or autoionization leads to formation of Br(+) and (energy permitting) Cl(+) fragment ions. Alternatively, the super-excited molecules can fragment to neutral atoms, one of which is in a Rydberg state. Complementary ab initio calculations lead to the conclusion that the observed [Cl**[(3)P(J)]4s + Br/Br*] products result from direct dissociation of the photo-prepared super-excited states, whereas [Br**[(3)P(J)]5p + Cl/Cl*] product formation involves interaction between the [A (2)Pi(1/2)]5ssigma and [X (2)Pi(1/2)]5psigma Rydberg potentials at extended Br-Cl bond lengths. Absorption of one further photon by the resulting Br** and Cl** Rydberg atoms leads to their ionization, and thus their appearance in the Br(+) and Cl(+) fragment ion images.     

Kinetics and mechanisms of bromine chloride reactions with bromite and chlorite ions

Chloride ion catalyzes the reactions of HOBr with bromite and chlorite ions in phosphate buffer (p[H(+)] 5 to 7). Bromine chloride is generated in situ in small equilibrium concentrations by the addition of excess Cl(-) to HOBr. In the BrCl/ClO(2)(-) reaction, where ClO(2)(-) is in excess, a first-order rate of formation of ClO(2) is observed that depends on the HOBr concentration. The rate dependencies on ClO(2)(-), Cl(-), H(+), and buffer concentrations are determined. In the BrCl/BrO(2)(-) reaction where BrCl is in pre-equilibrium with the excess species, HOBr, the loss of absorbance due to BrO(2)(-) is followed. The dependencies on Cl(-), HOBr, H(+), and HPO(4)(2)(-) concentrations are determined for the BrCl/BrO(2)(-) reaction. In the proposed mechanisms, the BrCl/ClO(2)(-) and BrCl/BrO(2)(-) reactions proceed by Br(+) transfer to form steady-state levels of BrOClO and BrOBrO, respectively. The rate constant for the BrCl/ClO(2)(-) reaction [k(Cl)(2)]is 5.2 x 10(6) M(-1) s(-1) and for the BrCl/BrO(2)(-) reaction [k(Br)(2)]is 1.9 x 10(5) M(-1) s(-1). In the BrCl/ClO(2)(-) case, BrOClO reacts with ClO(2)(-) to form two ClO(2) radicals and Br(-). However, the hydrolysis of BrOBrO in the BrCl/BrO(2)(-) reaction leads to the formation of BrO(3)(-) and Br(-).     

氯碘甲烷在A带的光解动力学

利用离子速度影像方法结合共振增强多光子电离(REMPI)技术研究了氯碘甲烷在A带的光解机理. 从266和277 nm的I*(5p 2P1/2)和I(5p 2P3/2)离子速度影像获得了碎片的平动能分布和角度分布. I和I*的平动能分布呈单高斯型, 可用软自由基近似来解释. I和I*是在排斥的势能面上直接解离产生的. 实验得到的各向异性参数β证实分子受激发后主要产生3Q0态, 并且3Q0和1Q1态之间存在非绝热转移. 波长越短, 这种非绝热转移越强. 在235 nm附近, Cl和Cl*各向同性的离子影像说明氯原子来自于CH2ICl的二次解离过程, 即CH2ICl先解离产生CH2Cl自由基, 自由基再解离产生氯原子.     

Influence of formation path on the CH2BrCl2+ dissociation dynamics

To get further insight into the CH2BrCl site-selective fragmentation previously observed upon inner-shell ionization, we have performed high-resolution Br 3d and Cl 2p Auger and spin-orbit resolved Br 3d Auger spectra, and studied the dissociation properties of the CH2BrCl2+ dication formed at threshold by means of threshold electron pair-ion coincidence measurements. The key point is that the origin of site-specific bond breaking is found in the Auger decay itself, as it preferentially populates selected dication states. Whereas the predominance of the C-Br bond breaking is observed in both threshold and inner-shell studies, no signature of selective C-Cl rupture is reported for the dication formed at threshold.     

F-loss and H-loss dissociations in low-lying electronic states of the CH3F+ ion studied using multiconfiguration second-order perturbation theory

Complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) calculations with an atomic natural orbital basis were performed for the 1(2)A', 1(2)A', 2(2)A', 2(2)A', and 3(2)A' (X2E, A2A1, and B2E) states of the CH3F+ ion. The 1(2)A' state is predicted to be the ground state, and the C(s)-state energy levels are different from those of the CH3Cl+ ion. The 2(2)A' (A2A1) state is predicted to be repulsive, and the calculated adiabatic excitation energies for 2(2)A' and 3(2)A' are very close to the experimental value for the B state. The CASPT2//CASSCF potential energy curves (PECs) were calculated for F-loss dissociation from the five C(s) states and H-loss dissociation from the 1(2)A', 1(2)A', and 2(2)A' states. The electronic states of the CH3+ and CH2F+ ions as the dissociation products were carefully determined by checking the energies and geometries of the asymptote products, and appearance potentials for the two ions in different states are predicted. The F-loss PEC calculations for CH3F+ indicate that F-loss dissociation occurs from the 1(2)A', 1(2)A', and 2(2)A' states [all correlating with CH3+(X1A1')], which supports the experimental observations of direct dissociation from the X and A states, and that direct F-loss dissociation can occur from the two Jahn-Teller component states of B2E, 2(2)A' and 3(2)A' [correlating with CH3+(1(3)A') and CH3+(1(3)A'), respectively]. Some aspects of the 3(2)A' Cl-loss PEC of the CH3Cl+ ion are inferred on the basis of the calculation results for CH3F+. The H-loss PEC calculations for CH3F+ indicate that H-loss dissociation occurs from the 1(2)A', 1(2)A', and 2(2)A' states [correlating with CH2F+(1(3)A'), CH2F+(X1A1), and CH2F+(1(1)A'), respectively], which supports the observations of direct dissociation from the X and B states. As the 2(2)A' H-loss PEC of CH3Cl+, the 2(2)A' H-loss PEC of CH3F+ does not lead to H + CH2X+, but the PECs of the two ions represent different types of reactions.     

Cl-loss and H-loss dissociations in low-lying electronic states of the CH3Cl+ ion studied using multiconfiguration second-order perturbation theory

To examine the experimentally suggested scheme of the pathways for Cl- and H-loss dissociations of the CH(3)Cl(+) ion in the X(2)E (1(2)A', 1(2)A' '), A(2)A(1) (2(2)A'), and B(2)E (3(2)A', 2(2)A") states, the complete active space-self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) calculations with an atomic natural orbital (ANO) basis were performed for the 1(2)A' (X(2)A'), 1(2)A", 2(2)A', and 2(2)A'" states. The potential energy curves describing dissociation from the four C(s) states were obtained on the basis of the CASSCF partial geometry optimization calculations at fixed C-Cl or C-H distance values, followed by the CASPT2 energy calculations. The electronic states of the CH3(+) and CH(2)Cl(+) ions produced by Cl-loss and H-loss dissociation, respectively, were carefully determined. Our calculations confirm the following experimental facts: Cl-loss dissociation occurs from the 1(2)A' (X(2)A'), 1(2)A", and 2(2)A' states (all leading to CH3(+) (X(1)A(1)') + Cl), and H-loss dissociation does not occur from 2(2)A'. The calculations indicate that H-loss dissociation occurs from the 1(2)A' and 1(2)A' ' states (leading to CH(2)Cl(+) (X(1)A(1)) + H and CH(2)Cl(+) (1(3)A") + H, respectively). The calculations also indicate that H-loss dissociation occurs (with a barrier) from the 2(2)A" state (leading to CH(2)Cl(+) (1(1)A") + H), supporting the observation of direct dissociation from the B state to CH(2)Cl(+) and that Cl-loss dissociation occurs from the 2(2)A" state (leading to CH3(+) (1(3)A") + Cl), not supporting the previously proposed Cl-loss dissociation of the B state via internal conversion of B to A. The predicted appearance potential values for CH3(+) (X(1)A(1)') and CH(2)Cl(+) (X(1)A(1)) are in good agreement with the experimental values.