Progressions In Ν1 Research Articles

Electronic, Raman and resonance Raman spectroscopy of [NBu4][RuBr4(MeCN)2

Raman spectra taken at resonance with the eu(Br pπ) → b2g(Ru dπ) charge-transfer (CT) transition of the trans-[RuBr4(MeCN)2]– ion, as its [NBu4]+ salt at ca. 80 K, consist of long overtone progressions in ν1(a1g), the symmetric RuBr stretch (at 188.5 cm–1), together with combination band progressions in which ν1 is the progression-forming mode and the enabling modes include ν2(b1g), νas(RuBr), and ν4(b2g), δs(BrRuBr). The excitation profile of the ν1 band approximately follows the contour of the eu → b2g CT transition referred to above, consistent with the operation of the A-term scattering mechanism. The spectroscopic data allow the determination of the harmonic wavenumber (ω1) and anharmonicity (x11) of the ν1(a1g) mode to be 188.8 cm–1 and –0.15 cm–1, respectively. Some comparative data on the analogous chloride ion, trans-[RuCl4(MeCN)2]–, are also given.

Emission spectroscopy of jet-cooled CS2 upon excitation of the Σg+1→1B2(1Σu+) transition in the 48 500–51 000 cm−1 region

The jet-cooled emission spectroscopy of gaseous carbon disulfide (CS2) was performed in the 48 500–51 000 cm−1 region in order to investigate changes in the early time dynamics of CS2 in the predissociative B21 (1Σu+) state. The spectra show emission into progressions of both the symmetric stretching (ν1) and bending (ν2) motions and combinations bands of these two motions. Analysis shows that the contribution of symmetric stretching and bending motion varies over the range of excitation wavelengths and the progression of ν2 decreases in intensity relative to the progression in ν1 as one scans through the energetic region near the barrier to linearity of this bent excited state molecule. We estimate the barrier height to be approximately 3400 cm−1 above the zero-point level of the B21 (1Σu+) state.

Resonance-Raman spectra and excited-state geometry of the bis(µ-acetato)(µ-oxo) ruthenium(III) dimeric ion [Ru2(µ-O2CMe)2(µ-O)(py)6]2+(py = pyridine)

The Raman spectra of [Ru2(µ-O2CMe)2(µ-O)(py)6][PF6]2(py = pyridine) at resonance with the π–π* transition at 588 nm of the Ru–O–Ru bridge display a progression in ν1, νsym(RuORu), 597 cm–1, reaching 5ν1 and five subsidiary progressions in ν1. The spectra and associated excitation profiles have been used in conjunction with a transform method to establish that the Ru–O bond length increases by ≈ 1.2 pm on excitation to this excited state.

Resonance Raman spectroscopy of the B1u region of benzene: Analysis in terms of pseudo-Jahn–Teller distortion

Raman spectra of benzene and benzene-d6 vapor obtained with excitation in the range from 208 to 188 nm are presented and discussed in terms of vibronic coupling of the resonant B1u state and the nearby E1u electronic state. The Raman spectra show strong activity in the binary overtones and combinations of the e2g modes ν8, ν9, and ν6 with the ν8 activity being dominant. (The Wilson numbering scheme for the modes of vibration is used throughout.) These bands, plus a progression in ν1 alone or in combination transitions involving two quanta of e2g modes, constitute the major intensity bands in the spectra. A simple first-order vibronic coupling model can be constructed which accounts adequately for most of the intensity in the Raman spectra observed in resonance with the B1u state, but this model results in a calculated absorption spectrum that is qualitatively different from that observed. The nature of the discrepancy indicates a significant Duschinsky mode rotation in the B1u state relative to the ground state. An analysis of the vibronic coupling of the B1u state with the nearby E1u state is performed using semiempirical calculation methods to provide excited state geometries, vibrational frequencies, and vibronic coupling parameters. This analysis confirms that there is strong vibronic coupling between these states resulting in a pseudo-Jahn–Teller effect. This results in a highly distorted potential surface for the B1u state with three D2h symmetry antiquinoidal minima lower in energy by ∼1000 cm−1 than the D6h symmetry geometry. The three minima of the threefold symmetric potential surface are separated by local maxima corresponding to the quinoidal geometry with a height of ∼300 cm−1. Three of the four e2g modes are calculated to have significant vibronic activity with mode 8 much stronger than modes 6 or 9. A small Jahn–Teller coupling is calculated. A strong Duschinsky rotation results from the vibronic activity of more than one mode. The absorption spectrum and the resonance Raman spectra calculated from this model are in good agreement with the experimental results. This analysis provides the first evidence for the expected pseudo-Jahn–Teller instability of the isolated 1B1u state of benzene.

Synthesis and spectroscopy of linear-chain palladium(II,IV) and platinum(II,IV) complexes involving quadridentate ligands

The effects of the in-plane ligand, the metal atom, the bridging halogen atom and the counter-anion on the electronic structures of a series of linear-chain, halogen-bridged, mixed-valence complexes of platinum and palladium have been investigated. Complexes of the type [ML][MLX2]Y4, where M = Pd or Pt, X = Cl, Br or I, L = 3, 7-diazanonane-1,9-diamine, 4,7-diazadecane-1,10-diamine, 1,4,8,11-tetraazacyclotetradecane or 1,4,8,12-tetraazacyclopentadecane and Y = BF4, ClO4 or PF6, have been examined by means of electronic, Raman and resonance-Raman spectroscopy. The electronic spectra of the complexes each show an intense intervalence charge-transfer band in the visible region, occurring at higher energy, Eg, than it does for analogous bis(ethylenediamine) complexes; this implies greater localisation of valences for the quadridentate than for the bis(ethylenediamine) complexes, in agreement with conclusions drawn from the X-ray structural results. Resonance-Raman spectra of the complexes display long progressions in the symmetric chain stretching mode ν1, νsym(X–MIV–X), corresponding members occurring at higher wavenumbers than for the analogous en complexes. Progressions in ν1 reach at most to v1= 12 for X = Cl, v1= 9 for X = Br and v1= 5 for X = I. Both the trends in Eg and also those in v1(max) vary in the order I < Br < Cl, Pd < Pt and BF4⩽ ClO4 < Pf6, implying increased valence localisation to the right in each series.

Photodissociation dynamics of jet-cooled ClNO on S1(1 1A″): An experimental study

We report measurements of photofragment yield (PHOFRY) spectra and NO E, V, R distributions following dissociation of jet-cooled ClNO on the S1(1 1A″) electronic surface. The dissociative S1(1 1A″)←S0(1 1A′) transition shows diffuse vibrational structure with a progression in ν1, the NO stretch. The absorption and PHOFRY spectra consist of two bands, corresponding to excitations into S1(000) and S1(100), whose widths are 1300±100 and 1000±70 cm−1, respectively. The relative partial absorption cross sections are S1(000):S1(100)=2.3:1.0. The narrowing of the absorption bands with increasing ν1 quanta is a consequence of the mismatch between ν1 and the free NO vibrational frequency. Dissociations on S1(000) and S1(100) yield NO in v″=0 and 1, respectively. The NO(X2∏) rotational distributions in v″=0 and 1 are inverted, peaking at J″∼30.5 with widths of 10±1 J″, and they do not vary significantly when the photolysis laser is scanned across the absorption band. The evolution of NO vibrational and rotational excitations appear to be largely uncoupled. In NO v″=0 and 1, the upper spin–orbit state 2∏3/2 is more populated than the lower state 2∏1/2. For both v″=0 and 1, the Λ-doublet ∏(A″) component of NO(2∏1/2) is more populated than the ∏(A′) component by a ratio of ∼3:1, as expected for excitation to a π* orbital of a″ symmetry, but this propensity is much lower for NO(2∏3/2), possibly due to perturbations with another surface. The absorption spectra and NO V, R distributions are in good agreement with recent dynamical calculations on a three-dimensional (3-D) potential-energy surface (PES) calculated ab initio. The vibrational distribution appears to be determined near the Franck–Condon (FC) region, while final-state interactions affect the rotational distributions at larger Cl–NO separations.

ChemInform Abstract: Infrared, Resonance‐Raman, and Excitation Profile Studies of (Os2(O2CCH2Cl)4Cl2), (Os2(O2CC2H5)4Cl2), and (Os2(O2CC3H7)4Cl2): Assignment of Osmium‐Osmium, Osmium‐Oxygen, and Osmium‐Chlorine Stretching Vibrations.

Detailed Raman (1 600–35 cm–1) and Fourier-transform i.r. (3 500–40 cm–1) studies of the diosmium tetracarboxylate complexes [Os2(O2CR)4Cl2](R = CH2Cl, C2H5, or C3H7), coupled with related earlier studies of [Os2(O2CCH3)4Cl2] and [Os2(O2CCD3)4Cl2], have provided a basis for the identification of the three Raman-active (a1g) bands ν1, ν2, and ν3 at 236–228, 393–256, and 311–292 cm–1 respectively, to the key skeletal fundamentals ν(OsOs), ν(OsO), and ν(OsCl), respectively. Thus, while both ν(OsOs) and ν(OsCl) are relatively insensitive to the carboxylate R group, ν(OsO) is, as expected, highly sensitive thereto. Raman studies at resonance with the intense near-ultraviolet electronic band (406–383 nm) of each complex yields resonance-Raman spectra in each case characterised by the development of three overtone progressions in ν1. These reach 6ν1, 4ν1+ν2, and 4ν1+ν3 at most. The results are typical of A-term resonance-Raman scattering. The depolarisation ratio of the ν1 band at resonance with the ca. 390 nm band demonstrates that the latter arises from an axially polarised transition, consistent with an earlier assignment π(Cl)→π*(Os2).

Neutral chain bromide- and iodide-bridged platinum(II,IV) complexes of 1,2-diaminoethane and thiocyanate: synthesis, electronic, infrared, Raman, and resonance-Raman studies

The complexes Pt(en)(SCN)2X, en = 1,2-diaminoethane, X = Br or I, have been synthesised and, on the basis of a study of their electronic, i.r., and resonance-Raman spectra, established to be linear-chain, halogen-bridged complexes, [Pt(en)(SCN)2][Pt(en)(SCN)2X2]. The electronic spectra are characterised by broad, intense bands (maxima at ca. 17 800 cm–1 for X = Br and at < 13 000 cm–1 for X = I). The i.r. spectra are near superpositions of those of the constituent complexes, the band shifts on complex formation being greater for the iodide-bridged complex. The resonance-Raman spectra are dominated by long overtone progressions in ν1, the Raman-active, symmetric (X–PtIV–X) stretch, reaching 7ν1 for X = Br or I. Subsidiary progressions v1ν1+νn are observed for X = Br, where νn is identified as ν(Pt–S)eq. The form of the resonance-Raman spectra, ν1 excitation profiles, and ν1 wavenumber dependence on the wavenumber of the exciting line, ν0, are discussed in terms of unresolved components of ν1 and of their relative intensity dependence on temperature and ν0.

Infrared, resonance-Raman, and excitation profile studies of [Os2(O2CCH2Cl)4Cl2], [Os2(O2CC2H5)4Cl2], and [Os2(O2CC3H7)4Cl2]: assignment of osmium–osmium, osmium–oxygen, and osmium–chlorine stretching vibrations

Detailed Raman (1 600–35 cm–1) and Fourier-transform i.r. (3 500–40 cm–1) studies of the diosmium tetracarboxylate complexes [Os2(O2CR)4Cl2](R = CH2Cl, C2H5, or C3H7), coupled with related earlier studies of [Os2(O2CCH3)4Cl2] and [Os2(O2CCD3)4Cl2], have provided a basis for the identification of the three Raman-active (a1g) bands ν1, ν2, and ν3 at 236–228, 393–256, and 311–292 cm–1 respectively, to the key skeletal fundamentals ν(OsOs), ν(OsO), and ν(OsCl), respectively. Thus, while both ν(OsOs) and ν(OsCl) are relatively insensitive to the carboxylate R group, ν(OsO) is, as expected, highly sensitive thereto. Raman studies at resonance with the intense near-ultraviolet electronic band (406–383 nm) of each complex yields resonance-Raman spectra in each case characterised by the development of three overtone progressions in ν1. These reach 6ν1, 4ν1+ν2, and 4ν1+ν3 at most. The results are typical of A-term resonance-Raman scattering. The depolarisation ratio of the ν1 band at resonance with the ca. 390 nm band demonstrates that the latter arises from an axially polarised transition, consistent with an earlier assignment π(Cl)→π*(Os2).

The photodissociation spectrum of SO+2

The photodissociation spectrum of SO+2 corresponding to the process SO+2 +hν→SO++O has been measured on a triple quadrupole system for the wavelength ranges: 3000–3400 and 4400–5120 Å. The spectrum in the visible has been assigned to the C̃ 2B1←Ã 2A2 transition and vibrational structure analyzed to yield λ00=4187 Å, the harmonic vibrational frequencies ν̃′1=953 cm−1, ν̃′′2=499 cm−1, ν̃′1=767 cm−1, and ν̃2 =410 cm−1, and the anharmonicity constants X″11 =−6.3 cm−1, X′′12 =−6.1 cm−1, X″22 =−4.2 cm−1, X12 =−6.3 cm−1, and X′22 =−7.4 cm−1. Apparent photodissociation cross sections ranged from ∼1×10−20–1.6×10−19 cm2 in the visible spectrum. In the UV spectrum the highly congested vibrational structure could not be resolved sufficiently for analysis; photodissociation cross sections ranged from ∼2–4×10−19 cm2 with broad bands roughly corresponding to expected progression in ν1 and ν′2 within the C̃ 2B1←X̃ 2A1 electronic transition. The process SO+2 +hν→S++O2 showed an onset near 3108 Å and the corresponding photodissociation spectrum showed sufficient vibrational structure to yield ν̃′′2∼454 cm−1, ν̃′1 ∼955 cm−1, and ν̃2 ∼411 cm−1. This new process, which had σ≤3×10−20 cm2, was proposed to result from the D̃ 2B2←X̃ 2A1 transition. Several new photodissociation cross section measurements on N2O+ have also been made in the vicinities of 3381 and 4880 Å, taking advantage of the high sensitivity (→10−21 cm2) of the triple quadrupole system.

Infrared and visible luminescence spectra of TcCl 2? 6 and TcBr 2? 6 in cubic crystals

The high-resolution infrared and visible luminescence spectra of TcCl2–6 and TcBr2–6 in several colourless cubic host crystals and of TcCl2–6 and K2PtCl6 and Cs2TeCl6 have been measured between 15 000 and 3500 cm–1 at temperatures down to 10 K. Five electronic transitions involving the four lowest components of the t32g configuration have been assigned, each showing detailed vibronic structure. Analysis of the structure of the visible emission enables the presence of progressions in ν1 but not in ν2 to be identified. This is interpreted as indicating that the luminescence arises from the Γ7 component of the 2T2g excited state, although the two spin–orbit components are close together in these compounds. For TcBr2–6 in Cs2TeCl6 and K2PtCl6 the excited states are populated by energy transfer.

The methylamine analogues of Wolffram's red and Reihlen's green: syntheses, infrared, electronic, Raman, and resonance-Raman spectroscopy, and X-ray crystal structures of chain chlorine- and bromine-bridged platinum(II,IV) complexes of methylamine

The syntheses and the electronic, i.r., Raman, and resonance-Raman spectra of the mixed-valence chain complexes [Pt(CH3NH2)4][Pt(CH3NH2)4X2][ClO4]4, where X = CI or Br, are reported. The electronic spectra are characterised by intense, broad intervalence bands whose maxima are at 24 100 and 18 200 cm–1, respectively. The i.r. spectra are near superpositions of those of the constituentions. The resonance-Raman spectra are dominated by long overtone progressions in ν1, the symmetric X–PtIV–X stretch, of up to nine members for X = Cl and seven for X = Br. The ω1 and x11 values for each complex are 324.8 ± 0.5 and –0.91 ± 0.07 cm–1, respectively, for X = Cl and 186.3 ± 0.4 and –0.14 ± 0.1 cm–1 for X = Br. The PtIV–X stretching force constants are 2.08 and 1.55 mdyn A–1 for X = Cl and Br, respectively, and the X–PtIV–X interaction constants are 0.074 and 0.057 mdyn A–1, respectively. The excitation profiles for the ν, bands maximise 1500–2800 cm–1 to the red of the PtII→ PtII intervalence band, as determined by transmission measurements. The crystal structures of the two complexes have been determined by single-crystal X-ray methods. In the bromide the structure contains ordered [⋯ PtII(CH3NH2)4⋯ Br–PtII(CH3NH2)4–Br ⋯] chains; the PtIV–Br and PtII–Br distances are 2.468(3) and 3.219(4)A, respectively, and the PtII–Br–PtIV angle is 165.4(3)°. The chloride structure contains an antiparallel disordering of the type of chain found in the bromide. The PtIV–Cl and PtII–Cl distances are 2.334(12) and 3.203(18)A, respectively, and the PtII–Cl–PtIV angle is 170.5(6)°. Both the spectroscopic and the crystallographic evidence indicate that the platinum-ion valences are localised in these complexes.

Synthesis, spectroscopy, and structure of the mixed-valence complexes [PtII(en)2][PtIV(en)2X2][PtIII 2(H2P2O5)4X2](en = 1,2-diaminoethane, X = Br or I)

The complexes [PtII(en)2][PtIV(en)2X2][PtIII2(H2P2O5)4X2](en = 1,2-diaminoethane) have been obtained as copper coloured needles (X = Br) or metallic green dichroic microcrystals (X = I) by the reaction of K4[PtII2(H2P2O5)4]·2H2O with [PtIV(en)2X2]X2 in aqueous solution at 100 °C. Spectroscopic evidence favours a formulation for the complexes which involves a halogen-bridged linear-chain PtII–PtIV cation in association with a dimeric PtIII anion. The absorption spectra are characterised by three bands, the one of lowest wavenumber being assigned to the PtII(dZ2)→ PtIV(dz2) intervalence transition of the chain cation and the next to the dσ→dσ* transition of the dimeric anion. The complexes are unusual in that they contain class II (partly-localised valence) cation chains while at the same time the interaction between the cation and anion is of the class I (highly-localised valence) type. The infrared, Raman, and resonance-Raman spectra of the two complexes have been studied in detail, the Raman spectra at ca. 80 K being characterised (among other things) by a progression [to 10ν1′(X = Br) and 5ν1′(X = I)] in the symmetric X–PtIV–X mode (ν1′) of the cation chain when the exciting line is at resonance with the PtII→ PtIV intervalence band, and by a progression (to 9ν1, X = Br or I) in the PtIII–PtIII stretching mode (ν1) of the anion at resonance with the σ→σ* transition. Single-crystal resonance-Raman spectra of the bromide at ca. 15 K show progressions in ν1′and ν1 as follows: v1′ν1′ to v1′= 11, v1v1 to v1= 12, v1ν1+ν2 to v1= 9, and v1ν1+ 2ν2 to v1= 8, where ν2 is the PtIII–Br symmetric stretching mode of the anion. The formulation for the complexes is unique in that it involves platinum in three different oxidation states.

The spectroscopy of dimethyl-s-tetrazine cooled in a supersonic free jet

The fluorescence excitation and dispersed emission spectra of dimethyl tetrazine have been observed in a supersonic free jet. Measurements of vibrational structure in the low resolution fluorescence excitation spectrum and in the single vibronic level emission spectrum have allowed us to confirm and extend vibrational assignments made in the static gas and solid matrix. The spectrum is dominated by progressions in the mode ν6a with strong progressions in ν1 as well. Excited vibrational levels of ν6a in the upper electronic state appear to be perturbed. The progression in ν1 is considerably more intense in dimethyl tetrazine than it is in tetrazine. The vibrational modes ν2, ν8a, ν16a, and ν16b have been assigned. Of these, the assignments of the first three agree with previous work, while the assignment of ν16b is at a much lower frequency. Rotational structure has been resolved at the origin band, and torsionless m=0 transitions have been assigned. Analysis of the m=0 levels indicates that the ring bond lengths and internal angles and their changes upon electronic excitation are similar to those of s-tetrazine and methyl-s-tetrazine.

On the nature of partially oxidised magnus green

The complex [Pt(NH3)4][Pt(NH3)4Cl2][HSO4]4 can be synthesised by the partial aerial oxidation of Magnus green in 50% sulphuric acid. It forms as highly dichroic, orange-red needles, which are shown to contain chlorine-bridged linear chains of the sort ⋯ PtII⋯ Cl–PtIV–Cl ⋯, the ammonia molecules being co-ordinated in the equatorial positions to each platinum atom. The resonance Raman spectrum of the complex at 80 K, obtained by irradiating within the contour of the intense PtIVâ†� PtII intervalence band, is dominated by a progression in ν1 to 11 ν1, where ν1 is the symmetric PtIV–Cl chain-stretching mode. The thermochromism of the complex is discussed. The nature of the other products of partial oxidation of Magnus green is also discussed.

Electronic, infrared, and resonance-Raman spectra of mixed-valence iodide-bridged linear-chain complexes of platinum

Electronic, i.r., and resonance-Raman (r.R.) spectra of mixed-valence complexes of platinum, [Pt(en)I2][Pt(en)I4], [Pt(en)2][Pt(en)2I2][ClO4]4, and cis-[Pt(NH3)2(SCN)2][Pt(NH3)2(SCN)2I2], where en = 1,2-diaminoethane, have been recorded as powders or discs at ca. 80 K. In addition, a single-crystal polarized r.R. spectrum of [Pt(en)2][Pt(en)2I2][ClO4]4 at room temperature has been obtained. Under r.R. conditions, progressions in ν1(120–123 cm–1), the symmetric X–PtIV–X stretching mode of the quadrivalent constituent, reach to 7, 9, and 8 members, respectively. The results confirm in the first two cases, and demonstrate in the last case, that the complexes are linear-chain iodide-bridged species. Brief results are also given on K4[PtI4][PtI6]. The excitation profiles of ν1 and 2ν1 of [Pt(en)I2][Pt(en)I4] and [Pt(en)2][Pt(en)2I2][ClO4]4 all maximize near to, but on the low-wavenumber side of, the intervalence band maximum. Those of ν1 and 2ν1 of the thiocyanate complex display a double maximum for which no explanation can be advanced.

ChemInform Abstract: ELECTRONIC SPECTRA, RESONANCE‐RAMAN SPECTRA, AND EXCITATION PROFILES OF THE MIXED‐VALENCE COMPOUND REIHLEN′S GREEN (PTII(C2H5NH2)4)(PTIVBR2(C2H5NH2)4)BR4.4H2O

The mixed-valence compound Reihlen's green, [PtII(C2H5NH2)4][PtIVBr2(C2H5NH2)4]Br4·4H2O, displays a resonance-Raman (r.r.) spectrum when irradiated within the contour of the mixed-valence charge-transfer transition in the visible. It is characterised by a progression in ν1, the Br–PtIV–Br symmetric breathing fundamental, which reaches 7ν1. Additional progressions nν1+ν2[where ν2 is the δ(Br–PtIV–N) bending fundamental] to n= 4 and nν1+ν3(where ν3 is probably a lattice mode) to n= 3 are also observed. The observation of such progressions permits the spectroscopic constants ω1, x11, x12, and x13 to be determined as 179.6, –0.37, 0.3, and 0.3 cm–1 respectively. The diffuse-reflectance spectrum of the compound indicates that there are two overlapped mixed-valence charge-transfer transitions in the visible (main band at 18 250 cm–1, shoulder at ca. 16 000 cm–1) both of which (on the basis of previous single-crystal work) are polarised parallel to the chain axis. The excitation profile of ν1(Stokes), 2ν1(Stokes), and ν1(anti-Stokes) have maxima at 16 100, 16 300, and 15 800 cm–1 respectively. The observation that axial vibrational modes are resonance-enhanced on irradiation of a compound with an exciting line whose frequency falls within the band contour of an axially polarised electronic transition is considered to be an important result which may open the way to making more precise assignments of the electronic spectra of many compounds.

Electronic spectra, resonance–Raman spectra, and excitation profiles of the mixed-valence compound Reihlen's green [PtII(C2H5NH2)4][PtIVBr2(C2H5NH2)4]Br4·4H2O

The mixed-valence compound Reihlen's green, [PtII(C2H5NH2)4][PtIVBr2(C2H5NH2)4]Br4·4H2O, displays a resonance-Raman (r.r.) spectrum when irradiated within the contour of the mixed-valence charge-transfer transition in the visible. It is characterised by a progression in ν1, the Br–PtIV–Br symmetric breathing fundamental, which reaches 7ν1. Additional progressions nν1+ν2[where ν2 is the δ(Br–PtIV–N) bending fundamental] to n= 4 and nν1+ν3(where ν3 is probably a lattice mode) to n= 3 are also observed. The observation of such progressions permits the spectroscopic constants ω1, x11, x12, and x13 to be determined as 179.6, –0.37, 0.3, and 0.3 cm–1 respectively. The diffuse-reflectance spectrum of the compound indicates that there are two overlapped mixed-valence charge-transfer transitions in the visible (main band at 18 250 cm–1, shoulder at ca. 16 000 cm–1) both of which (on the basis of previous single-crystal work) are polarised parallel to the chain axis. The excitation profile of ν1(Stokes), 2ν1(Stokes), and ν1(anti-Stokes) have maxima at 16 100, 16 300, and 15 800 cm–1 respectively. The observation that axial vibrational modes are resonance-enhanced on irradiation of a compound with an exciting line whose frequency falls within the band contour of an axially polarised electronic transition is considered to be an important result which may open the way to making more precise assignments of the electronic spectra of many compounds.

Vibronic spectra of the ozonide ion in the matrix-isolated M+O3− species

Matrix reactions of alkali metal atoms and ozone molecules at high dilution in inert gases produced a clear yellow film during condensation at 10–22 K on a sapphire plate which yielded vibronic spectra of the M+O3− species. Best resolution of up to 14 vibronic bands spaced 800–900 cm−1 apart was obtained for the lithium and sodium compounds. These bands formed a strong progression in ν1′ and the first six bands exhibited the presence of a weaker progression in ν2′. The band origin was located at 17 730 cm−1 for Li+16O3− and Li+18O3− in solid krypton. Harmonic and anharmonic vibrational constants were determined graphically for the excited electronic state.

Analysis of the 2973-Å Absorption System of Phosgene

The near-ultraviolet absorption of phosgene has been assigned to a π* ← n, 1A2 ← 1A1, electronic transition from vapor-phase spectra recorded under conditions of high resolution and low temperature. Progressions in ν1′, ν2′, ν3′, ν4′, and ν4″ have been identified in the spectrum and have been analyzed in terms of vibronic transitions between a planar ground and a nonplanar excited state. A barrier height of 3170 cm−1 and a nonplanar equilibrium angle of 32.5° were calculated for the upper state from a fit of the energy levels of a Lorentzian–quadratic potential function to the observed levels of ν4. The false origin, 401, of the spectrum has been assigned to the band at 33 631 cm−1. An oscillator strength of f = 1.04 × 10−3 has been obtained for the A21 ← A11 transition.