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This chapter presents 19 problems covering the subject of bioinorganic chemistry, along with their corresponding solutions.

This chapter presents 20 problems covering the subject of bonding and reactivity of metal clusters, along with their corresponding solutions.

This chapter presents 23 problems covering the subject of atomic orbitals, along with the corresponding solutions.

This chapter presents 32 problems covering the subject of transition metal chemistry, along with their corresponding solutions.

This chapter presents 47 problems covering the subject of crystal structure, along with their corresponding solutions.

This chapter presents 22 problems covering the subject of vibrational spectroscopy, along with the corresponding solutions.

This chapter presents 52 problems covering the subject of molecular geometry and bonding, along with the corresponding solutions.

This chapter presents 41 problems covering the subject of crystal field theory, along with the corresponding solutions.

This chapter presents 23 problems covering the subject of molecular symmetry, along with the corresponding solutions.

The First Edition of this book, which appeared in 2013, serves as a problem text for Part I (Fundamentals of Chemical Bonding) and Part II (Symmetry in Chemistry) of the book Advanced Structural Inorganic Chemistry published by Oxford University Press in 2008. A Chinese edition was published by Peking University Press in August in the same year. Since then the authors have received much feedback from users and reviewers, which prompted them to prepare a Second Edition for students ranging from freshmen to senior undergraduates who aspire to attend graduate school after finishing their first degree in Chemistry. Four new chapters are added to this expanded Second Edition, which now contains over 400 problems and their solutions. The topics covered in 13 chapters follow the sequence: electronic states and configurations of atoms and molecules, introductory quantum chemistry, atomic orbitals, hybrid orbitals, molecular symmetry, molecular geometry and bonding, crystal field theory, molecular orbital theory, vibrational spectroscopy, crystal structure, transition metal chemistry, metal clusters: bonding and reactivity, and bioinorganic chemistry. The problems collected in this volume originate from examination papers and take-home assignments that have been part of the teaching program conducted by senior authors at The Chinese University of Hong Kong over nearly a half-century. Whenever appropriate, source references in the chemical literature are given for readers who wish to delve deeper into the subject. Eight Appendices and a Bibliography listing 157 reference books are provided to students and teachers who wish to look up comprehensive presentations of specific topics.

This chapter presents 33 problems covering the subject of introductory quantum chemistry, along with the corresponding solutions.

This chapter presents 29 problems covering the subject of electronic states and configurations of atoms and molecules, along with the corresponding solutions.

The Gaussian-3 (G3) and Gaussian-3X (G3X) models of theory have been used to calculate the thermochemical data for chlorine fluorides ClFn, n = 1−7, as well as for their singly charged cations and anions. The quantities calculated include the heats of formation (ΔHf) and bond dissociation energies (DEs) of all of the species, as well as the ionization energies (IEs) and electron affinities (EAs) of the neutrals. By comparing the well-established experimental data of ClF and ClF3 with the G3 and G3X results, it is found that the G3X method yields more accurate ΔHf values. In addition, the G3 values on the IEs and EAs for ClF and ClF3 are similar to the corresponding G3X results. On the basis of these findings, the G3X results are used to assess the sometimes conflicting experimental data. The fair to excellent agreement between the known experimental values and the G3X results also lends support to our predictions for the missing experimental thermochemical data of chlorine fluorides and their ions. Furthe...

The vacuum ultraviolet pulsed field ionization-photoelectron spectra of supersonically cooled cis-2-butene (cis-CH3CH=CHCH3) have been measured in the photon energy range of 73 560–75 460 cm−1. Using the ab initio theoretical rotational constants of cis-CH3CH=CHCH3 and its cation (cis-CH3CH=CHCH3+) and a semiempirical simulation scheme, we have obtained a good fit of the origin vibrational band with partially resolved contours of rotational branches. After taking into account the Stark shift, the ionization energy of cis-CH3CH=CHCH3 is determined to be 73 595.0±1.5 cm−1. Guided by ab initio vibrational frequency calculations, we have also assigned the vibrational bands observed for cis-CH3CH=CHCH3+ in its ground state.

The C–H⋯N hydrogen bond in the methane–ammonia complex is studied by determining its bond dissociation energy (BDE) and the n(N)→σ ∗ (C–H) interaction. At the MP2(Full)/6-311++G(3df,2p) level of theory with basis set superposition error (BSSE) correction, the BDE was determined to be 2.5 kJ mol−1. The n(N)→σ ∗ (C–H) interaction at this level of theory was found to be 3.7 kJ mol−1 by natural bond orbital (NBO) analysis. It was also found that the NBO values are in general higher than the BDE values with BSSE correction when they are compared at the same level of theory.

Gaussian-2 ab initio calculations were performed to examine the six modes of unimolecular dissociation of cis-CH3CHSH+ (1+), trans-CH3CHSH+ (2+), and CH3SCH2+ (3+): 1+→CH3++trans-HCSH (1); 1+→CH3+trans-HCSH+ (2); 1+→CH4+HCS+ (3); 1+→H2+c-CH2CHS+ (4); 2+→H2+CH3CS+ (5); and 3+→H2+c-CH2CHS+ (6). Reactions (1) and (2) have endothermicities of 584 and 496 kJ mol−1, respectively. Loss of CH4 from 1+ (reaction (3)) proceeds through proton transfer from the S atom to the methyl group, followed by cleavage of the C–C bond. The reaction pathway has an energy barrier of 292 kJ mol−1 and a transition state with a wide spectrum of nonclassical structures. Reaction (4) has a critical energy of 296 kJ mol−1 and it also proceeds through the same proton transfer step as reaction (3), followed by elimination of H2. Formation of CH3CS+ from 2+ (reaction (5)) by loss of H2 proceeds through protonation of the methine (CαH) group, followed by dissociation of the H2 moiety. Its energy barrier is 276 kJ mol−1. On both the MP2/6-31G* and QCISD/6-31G* potential-energy surfaces, the H2 1,1-elimination from 3+ (reaction (6)) proceeds via a nonclassical intermediate resembling c-CH3SCH2+ and has a critical energy of 269 kJ mol−1.

Gaussian-2 ab initio method was performed to examine the five modes of unimolecular dissociation of CH 3 SCH 2 + ( 1 + ) and CH 2 CHSH 2 + ( 5 + ): 1 + →CH 3 +H 2 CS + (1); 1 + →CH 3 + +H 2 CS (2); 1 + → CH 4 +HCS + (3); 5 + →H 2 S + [C 2 H 3 ] + (4); and 5 + →H 3 S + +C 2 H 2 (5). Both reactions 1 and 2, with endothermicities 359 and 395 kJ mol −1 respectively, proceed without a reverse barrier. Loss of CH 4 from 1 + (reaction 3) proceeds via a transition state resembling an ion–radical complex CH 3 /H 2 CS + . The elimination reaction has an energy barrier of 332 kJ mol −1 . Loss of H 2 S from 5 + (reaction 4) initially proceeds through either cleavage of the C–S bond or formation of the ion–molecule complex H 2 S/[C 2 H 3 ] + ( 8 + / 9 + ), followed by dissociation of the complex. The endothermicity of reaction 4 is calculated to be 245–261 kJ mol −1 . Reaction 5, the lowest energy process among the dissociation pathways studied in this work, proceeds via intermediates 9 + and H 3 S + /C 2 H 2 ( 10 + ). Its rate-determining step 5 + → 9 + has an energy barrier of 220 kJ mol −1 .

The heats of formation for the five (CH)6 isomers have been calculated using both the atomization and isodesmic bond separation schemes at the following six theoretical levels: G2(MP2,SVP), G2(MP2), G2(MP3), G2, CBS-Q, and CBS-APNO. It is found that, with the isodesmic scheme, all four G2-based methods give ΔHf values that are within a few kJ mol−1 of each other. In particular, the G2(MP2,SVP) and G2 yield the most accurate ΔHf values for benzene, the only isomer whose listed experimental data are suitable for comparison with ab initio results. For the CBS-Q and CBS-APNO levels, the isodesmic scheme gives worse results than the atomization scheme, but the results from the two levels are more consistent in the isodesmic scheme. These results suggest that a combination of either the G2(MP2,SVP) or G2 model with the isodesmic scheme should afford accurate thermochemical data for relatively large hydrocarbon compounds. At the G2 level, using the isodesmic bond separation scheme, we obtain the following ΔHf0 values (in kJ mol−1) for the five (CH)6 isomers: 100.5 for benzene (compared to the experimental value of 100.4±1), 415.5 for Dewar benzene, 567.2 for prismane, 397.5 for benzvalene, and 593.6 for 3,3′-bicyclopropenyl. At the same level and with the same scheme, the calculated ΔHf298 values (in kJ mol−1) are: 82.0 for benzene (compared to the experimental value of 82.9±0.3), 397.1 for Dewar benzene, 547.0 for prismane, 378.1 for benzvalene, and 578.8 for 3,3′-bicyclopropenyl.

The potential energy surface of [C2H5S+] ions was studied with the G2 method. The structures and G2 heats of formation (ΔHf0) of CH3CH2S+ (1+), syn-CH3CHSH+ (2+), anti-CH3CHSH+ (3+), and CH3SCH2+ (4+) were reported previously (1993, Chem. Phys. Lett., 213, 250). The G2 ΔHf298=802 kJ mol−1 of c-CH2CH2SH+ (7+) is in good agreement with the experimental ΔHf298 (7+)=798 kJ mol−1 (1988, J. Phys. Chem. Data, Suppl. 1). The symmetric conformer of protonated vinyl thiol CH2CHSH2+ (ΔHf0 (9+)=857 kJ mol−1) is slightly more stable than the non-symmetric one (8+) by 8 kJ mol−1. The C–C protonated thiirane 11+ with ΔHf0=989 kJ mol−1 is an intermediate for the 1,3-H shift 4+→4+. The isomerization reactions 8+/9+→2+/3+→7+→4+ are energetically facile compared to the unimolecular dissociation processes. The ΔHf0 of the transition state structures for these isomerizations lies within a narrow range of 960–1000 kJ mol−1. The calculated energetics of [C2H5S+] are in line with the observation (1979, Org. Mass Spectrom. 14, 543) that both 2+/3+ and 4+ isomerize to a common structure 7+ and decompose through the same reaction channels.

The vacuum ultraviolet (VUV) pulsed field ionization photoelectron (PFI-PE) spectra for CH3SH and CH3CH2SH have been obtained near their ionization thresholds. Using a semiempirical simulation scheme, we have obtained satisfactory fits to fine structures resolved in the VUV-PFI-PE spectra, yielding accurate ionization energies of 76 256.3±2.9 cm−1 (9.454 58±0.000 36 eV) and 74 948.7±2.9 cm−1 (9.292 46±0.000 36 eV) for CH3SH and CH3CH2SH, respectively.

The potential energy surface of C2H5S isomers has been studied with the G2 ab initio method. The structures and G2 heats of formation of the six stable isomers/conformers, CH3CH2S (1), syn-CH3CHSH (2), anti-CH3CHSH (3), CH3SCH2 (4), gauche-HSCH2CH2 (5), and anti-HSCH2CH2 (6), have been reported previously (Chem. Phys. Lett., 213 (1993) 250; J. Chem. Phys., 104 (1996) 130). Their structural properties upon change of conformation can be rationalized by the perturbative molecular orbital model. The C2H5S radicals are very flexible due to low-energy barriers for rotations and inversions. Unimolecular rearrangements are exclusively 1,2- and 1,3-H shifts with large G2 activation energies at 0 K: Ea(1 → 3) = 147.0 kJ mol−1, Ea(1 → 5) = 140.0 kJ mol−1, Ea(2 → 5) = 187.2 kJ mol−1, Ea(3 → 6) = 191.7 kJ mol−1, and Ea(4 → 4) = 176.9 kJ mol−1. The TS structures for the unimolecular decompositions: 5 → C2H4 + SH (6), 1 → CH3 + H2CS (7), and 4 → CH3 + H2CS (8) are loose and product-like. Their UHF determinant functions have considerable spin contamination (〈S2〉 ≈ 0.96–1.08). Energy barriers for the analogous reactions of 6 and 7 for the oxygen analogs were also computed and compared to the observed rate parameters. In general, it is found that the G2 method is still reliable to estimate the reaction barriers for systems with 〈S2〉 ≤ 0.96. Correction with spin projection is required for systems with 〈S2〉 > 1.0. Among the reactions of C2H5S studied in this work, the pathway with the lowest energy is 6. The G2 Ea = 41.7 kJ mol−1 for 6 at 700 K is in good agreement with Shum and Benson's (Int. J. Chem. Kinet., 17 (1985) 277, 749) estimated value (46 kJ mol−1). At the same temperature, the calculated Ea′s for 7 and 8, after spin-projection corrections, are 158.9 kJ mol−1 and 109.0 kJ mol−1, respectively, in agreement with the estimated Ea's (145.5 kJ mol−1 for 7 and 101.3 kJ mol−1 for 8). The addition reaction CH 3 + H 2 CS → 4 ( 8 ) is predicted to be negative temperature dependent with an Eaof −3.0 kJ mol−1 at 700 K. This is in line with the lower bound of the estimated Ea(ca. 11.7 kJ mol−1 ± 12.6 kJ mol−1) for 8 at 644 K as reported by Shum and Benson.

High-resolution photoionization efficiency (PIE) and pulsed field ionization photoelectron (PFI-PE) spectra for CS2 have been measured using coherent vacuum ultraviolet (VUV) laser radiation in the energy range of 81 050–82 100 cm−1. The PIE and threshold photoelectron (TPE) spectra for CS2 in the energy range of 80 850–82 750 cm−1 have also been obtained using synchrotron radiation for comparison with results of the VUV laser study. The analysis of the PIE spectra reveals three Rydberg series converging to the excited CS2+(2Π1/2) spin–orbit state. These series, with quantum defects of 1.430, 1.616, and 0.053, are associated with the [2Π1/2]npσu, [2Π1/2]npπu, and [2Π1/2]nfu configurations, respectively. The Stark shift effect on the ionization threshold of CS2 has been examined as a function of dc electric fields (F) in the range of 0.65–1071 V/cm. The observed F dependence of the Stark shift for the ionization onset of CS2 is consistent with the prediction by the classical adiabatic field ionization form...

The kinetic energy release spectra for SH resulting from the 193 nm laser photofragmentation of HSCH2CH2SH have been measured. On the basis of the observed maximum kinetic energy for the formation of HS+CH2CH2SH, a value of 74±2 kcal/mol is derived for the bond dissociation energy of HS–CH2CH2SH at 0 K [D0(HS–CH2CH2SH)]. Angular distribution measurements for SH yield an anisotropic parameter β=−0.4±0.1 for the HS+CH2CH2SH channel, indicating that the C–S bond fission is fast with respect to molecular rotation. The energetics for the formation of HS+CH2CH2SH from HSCH2CH2SH have been investigated using the Gaussian‐2 (G2) and G2(MP3) ab initio quantum chemical procedures. The G2/G2(MP3) calculations give a prediction of 72.5 kcal/mol for D0(HS–CH2CH2SH), in excellent agreement with the experimental value. Ab initio first‐order configuration interaction calculations have also been made to examine the possible excited state of HSCH2CH2SH involved in the photodissociation process and to rationalize the observ...

The potential energy surface of FCP was studied with high-level single-reference electron correlated optimization. It was found that linear FPC is a potential energy minimum at the RMP2 and RMP4 levels of theory but a maximum at UMP2, RPM3, UMP3 and UMP4. Moreover, various numbers of minima (Min) and saddle points (TSs) were found on the restricted and unrestricted MPn (n = 2–4) surfaces: 3 Min and 2 TSs on RMP2, 3 Min and 3 TSs on UMP2, 2 Min and 2 TSs on RMP3, 3 Min and 3 TSs on UMP3, 3 Min and 2 TSs on RMP4, and 3 Min and 3 TSs on UMP4. However, at the more reliable quadratic CI and Brueckner doubles levels of theory, only two minima, corresponding to linear FCP and bent FPC (bond angle about 110 °), and two saddle points were found on the potential energy surface.

The comparison of the experimental thermochemical data and G2 or [G2(MP2)] predictions for SF{sub n}, SF{sub n}{sup +}, and SF{sub n} {sup -} (n = 1-6) allows us to recommend a self-consistent set of experimental {Delta}{sub f}H{degree}{sub 0}, IE, EA, D{degree}{sub 0} values for these systems. This work shows that for reliable determinations of the thermochemical data for a complex system such as SF{sub n}, SF{sub n} {sup +}, and SF{sub n}{sup -} (n = 1-6), it is necessary to combine experimental measurements made using different techniques and theoretical predictions calculated using a sufficiently accurate theoretical procedure. The comparison of experimental and theoretical results in this study further confirms that G2 and G2(MP2) procedures are reliable theoretical methods for providing energetic predictions accurate to 4-5 kcal/mol for complex sulfur-containing molecular species. The theoretical equilibrium structures obtained for SF{sub n}, SF{sub n}{sup +}, and SF{sub n}{sup -} (n = 1-6) have been rationalized using the VSEPR theory. Furthermore, we have provided an explanation to account for the observed alternating patterns in IE, EA, and D{degree}{sub 0} values for SF{sub n}, SF{sub n}{sup +}, and SF{sub n}{sup -} (n = 1-6). Alternating patterns in IE, EA, and D{degree}{sub 0} values are expectedmore » for other similar hypervalent species. 60 refs., 2 figs., 4 tabs.« less

The energetics and structures for isomers of the CH 3 S 2 , CH 3 S 2 + , and CH 3 S 2 − systems have been studied with the ab initio Gaussian-2 (G2) method. At the MP2(full)/6-31G(d) level, there are five minima on the potential energy surface of CH 3 S 2 , corresponding to equilibrium structures CH 3 SS, CH 2 SHS, CH 2 SSH, HSCH 2 S and HSCHSH. At the same level of theory, CH 3 S 2 + may exist as six isomers: CH 3 SS + , CH 2 SHS + , CH 2 SSH + , c-HSCH 2 S + , HSCHSH + and CHSHSH + ; CH 3 S 2 − may exist as four isomers: CH 3 SS − , CH 2 SHS − , HSCH 2 S − and HSCHSH − . The most stable CH 3 S 2 , CH 3 S + 2 and CH 3 S 2 − species are CH 3 SS, HSCHSH + and CH 3 SS − , respectively. Transition structures for the rearrangements of the neutral radicals and the cations are also located. The structures and energetics of all the species located are discussed. Also, the G2 standard molar enthalpies of formation and ionization energies of various species are in good agreement with the available experimental data.

By carrying out Gaussian-2 calculations, which is an approximation to the ab initio level of QCISD(T)/6-311+G(3df,2p), the potential energy surfaces of the CH 3 O 2 and CH 3 O 2 + systems have been constructed. At the MP2(full)/6-31G(d) level, CH 3 O 2 may exist as six stable isomers: HOCHOH ( C 1 ) ( 1 ), OCH 2 OH ( C 1 ) ( 2 ), CH 3 OO ( C s ) ( 3 ), CH 2 OOH ( C 1 ) ( 4 ), CH 2 OHO ( C 1 ) ( 5 ) and CH 2 O ··· HO ( C s ) ( 6 ), while CH 3 O 2 + may exist as eight isomers: HOCHOH + ( C s ) ( 1 + ), cyclic-OCH 2 OH + ( C 1 ) ( 2 + ), CH 3  OO + ( C s ) ( 3 + ), CH 2 OOH + ( C s ) ( 4 + ), CH 2  OHO + ( C 1 ( 5 + ), cyclic-HOCHOH + ( C 1 ) ( 6 + ), H 2 O ··· CHO + ( C s ) ( 7 + ) and OH 3 ··· CO ( C s ) ( 8 + ). The most stable CH 3 O 2 and CH 3 O 2 + species are HOCHOH and HOCHOH + , respectively. Transition structures for the rearrangements of the radicals and cations were also located. The structures and energetics of all the species located are discussed. The Gaussian-2 results are in excellent agreement with the available experimental data.

This chapter presents 68 problems covering the subject of molecular orbital theory, along with the corresponding solutions.

By means of a geometry optimization at the MP2/6-31G(d) level, the CH 3 O 2 radicals have been found to exist in five isomeric forms. In order of decreasing stabilities, they are: HOCHOH ( 1 ) > OCH 2 OH ( 2 ) > CH 3 OO ( 3 ) > CH 2 OOH ( 4 ) > CH 2 OHO ( 5 ). On the other hand, there are six CH 3 O 2 + isomers: HOCHOH + ( 1 + ) > CH 2 OOH + ( 4 + ) > cyclic-OCH 2 OH + ( 2 + > CH 3 OO + ( 3 + ) #62; CH 2 OHO + ( 5 + ) > cyclic-HOCHOH + ( 6 + ). The Gaussian-2 predictions for the heats of formation at 298 K are in agreement with available experimental values.

By combining molecular beam photodissociation and photoionization measurements with ab initio Gaussian‐2 (G2) calculations on the CH3S2 and CH3S+2 systems, we have shown that CH3SS is the dominant isomer formed in the photodissociation process, CH3SSCH3+hν(193 nm) →CH3S2+CH3. The experimental ionization energy for CH3SS (8.97±0.02 eV) and the heat of formation at 0 K for CH3SS+ (217.7±1.2 kcal/mol) are in excellent agreement with the G2 results. The photoionization efficiency spectrum observed for CH3SS is also consistent with the theoretical prediction that the Franck–Condon factor for the photoionization process, CH3SS+hν →CH3SS++e−, is not favorable. Based on the statistical modeling of experimental rates obtained previously for HS loss in the unimolecular decomposition of CH3SSCH+3 and the comparison with G2 ab initio predictions, we conclude that CH2SSH+ is most likely the isomer structure formed near the experimental appearance energy (11.07 eV) observed for the photodissociative ionization process, CH3SSCH3+hν→CH3S+2+CH3+e−.

The potential energy surface for the GaH4 radical was investigated using ab initio MO theory. Three minima corresponding to equilibrium structures with D2d, C3v and Cs, symmetry were found. The D2d and C3v structures are 144 and 95kJmol− above the Cs structure, respectively. From both structural and energetic points of view, the Cs structure is likely to be a weak van der Waals molecular complex between GaH2 and H2, which may easily dissociate into these two fragments.

The structure and energetics for CH{sub 3}SSCH{sub 2} and CH{sub 3}SF have been investigated at the Gaussian-2 level of ab initio theory. The calculated ionization energies for CH{sub 3}SSCH{sub 2} and CH{sub 3}SF are found to be in excellent agreement with the experimental measurements of Baker and Dyke. 13 refs., 1 fig., 2 tabs.

Accurate ionization energies (IE`s) for molecular species are used for prediction of chemical reactivity and are of fundamental importance to chemists. The IE of a gaseous molecule can be determined routinely in a photoionization or a photoelectron experiment. IE determinations made in conventional photoionization and photoelectron studies have uncertainties in the range of 3--100 meV (25--250 cm{sup {minus}1}). In the past decade, the most exciting development in the field of photoionization and photoelectron spectroscopy has been the availability of high resolution, tunable ultraviolet (UV) and vacuum ultraviolet (VUV) laser sources. The laser pulsed field ionization photoelectron (PFI-PE) scheme is currently the state-of-the-art photoelectron spectroscopic technique and is capable of providing photoelectron energy resolution close to the optical resolution. The author has focused attention on the photoionization processes of some sulfur-containing species. The studies of the photoionization and photodissociation on sulfur-containing compounds [such as CS{sub 2}, CH{sub 3}SH, CH{sub 3}SSCH{sub 3}, CH{sub 3}CH{sub 2}SCH{sub 2}CH{sub 3}, HSCH{sub 2}CH{sub 2}SH and C{sub 4}H{sub 4}S (thiophene) and sulfur-containing radicals, such as HS, CS, CH{sub 3}S, CH{sub 3}CH{sub 2}S and CH{sub 3}SS], have been the major subjects in the group because sulfur is an important species contributing to air pollution in the atmosphere. Themore » modeling of the combustion and oxidation of sulfur compounds represents important steps for the control of both the production and the elimination of sulfur-containing pollutants. Chapter 1 is a general introduction of the thesis. Chapters 2 and 6 contain five papers published in, or accepted for publication in, academic periodicals. In Chapter 7, the progress of the construction in the laboratory of a new vacuum ultraviolet laser system equipped with a reflectron mass spectrometer is presented. Chapters 2 through 7 have been removed for separate processing. A general conclusion of these studies are given in Chapter 8 followed by an appendix.« less

Using the same level of ab initio quantum chemical theory as that applied by Becker et al. [J. Chem. Phys. 100, 1759 (1994)], we have reexamined the structures of SF5 and SF+5. Contrary to their report, we find that the SF5/(D3h) and SF+5(C4v) structures are not local minima. The adiabatic ionization energies (IE) for SF4 and SF5, and the heats of formation at 0 K (ΔHf00) for SF4, SF+4, SF5, SF+5, and SF6 have also been calculated using the G2(MP2) procedure [Curtiss et al., J. Chem. Phys. 98, 1293 (1993)]. Excellent agreement is found between the theoretical G2(MP2) and accepted experimental IEs for SF4 and SF5. The theoretical ΔHf00’s for SF4, SF+4 and SF6 are also in excellent accord with the literature values. However, the G2(MP2) calculation indicates that the current recommended experimental ΔHf00(SF5) may be too low by about 10 kcal/mol.

The rearrangement of the fulminate anion (CNO¯) to the cyanate anion (OCN¯) has been studied with high-level ab initio methods. Geometry optimizations have been carried out at HF, MPn (n = 2-4), QCISD, QUISD(T), BD and BD(T) levels using the 6-31+G(d) basis set. The highest level of theory for the calculation of relative energies is QCISD(T)/6-311+G(3df, 2p). Results show that the rearrangement proceeds via an oxazirinyl anion intermediate, which is separated by barriers of 52·8 and 18·4 kJ mol-1 from CNO¯ and OCN¯, respectively.