Direct absorption measurement of the spin—orbit splitting of the ground state in atomic fluorine

We have measured the three hyperfine components of the spin—orbit split (²P_{$\text{3}\text{2}$} → ²P_{$\text{1}\text{2}$}) ground state in atomic fluorine by diode laser absorption spectroscopy. The measurement improves the accuracy of the two lines previously reported (404.175 and 403.969 cm^?1), with the third line at 404.210 cm^?1. This confirms the spacing of the hyperfine components measured by EPR, and establishes diode laser absorption as a viable technique for determining F-atom concentrations.     

Direct observation of the spinorbit splitting in the Ar+ ion with a diode laser

The ²P_{$\text{1}\text{2}$}-²P_{$\text{3}\text{2}$} fine structure transition in the ground (3p⁵) state of the argon atomic ion. Ar⁺, has been detected in absorption using a tunable diode laser. The transition was calibrated against water vapour lines and measured to be 1431.644 ± 0.001 cm^?1 in ⁴⁰Ar⁺ and 3.0 × 10^?3 cm^?1 (91 MHz) smaller in ³⁶Ar⁺.     

Two-photon spectra of gases by three-wave mixing

We show that the two-photon resonances in the third-order susceptibility can be exploited to yield two-photon spectra of molecular gases at moderately high spectral resolution. This form of spectroscopy does not depend on the occurrence of processes (such as fluorescence of photoionization) leading to indirect methods of two-photon absorption. The method is direct and leads in principle to values for a two-photon cross section. Comparisons of two-photon and coherent anti-Stokes Raman resonances leads to ratios of Raman and two-proton cross sections independent of the laser powers and spatial characteristics. The technique is documented with rotationally resolved spectra of SO₂ and NO. A value for |α_xxα_yy| of 1.5 × 10^?52 cm⁶ was measured for the O₁₂ (6$\text{built:1}\text{2}$) component of the (A)²Σ ← (X)² Π_{$\text{1}\text{2}$} transition of nitric oxide.     

Yield of I(2Psol:12) in the photodissociation of CH2I2

The production of I(²P_{$\text{1}\text{2}$}) in the photolysis of CH₂I₂ has been studied optoacoustically at excitation wavelengths between 365.5 and 247.5 nm. Bands found at 32200 and 47000 cm^?1 correlate with I(²P_{$\text{3}\text{2}$}) whilst those at 34700 and 40100 cm^?1, which correlate with I(²P_{$\text{1}\text{2}$}), give final ²P_{$\text{3}\text{2}$}/²P_{$\text{1}\text{2}$} ratios of 1.75 and 1.1, respectively, after curve crossing.     

The importance of spin relaxation in the delayed fluorescence of molecular crystals

Deactivation rate constants of spin-orbital excited Br atoms in the reactions Br(²P_{$\text{1}\text{2}$}) + O₂ → Br(²P_{$\text{3}\text{2}$}) + O₂ (k₁), and Br(²P_{$\text{1}\text{2}$}) + NO → Br(²P_{$\text{3}\text{2}$}) + NO (k₄) have been measured with a photodissociative IBr laser on the electronic transition ²P_{$\text{1}\text{2}$}?²P_{$\text{3}\text{2}$} in the Br atom (λ = 2.7 μm). The values obtained are (6.4 ± 1.8) × 10^?14 cm³ s^?1 and (1.9 ± 0.6) × 10^?12 cm³ s^?1, respectively. Comparison with published data leads to the conclusion that, contrary to a widely accepted point of view, the high rate constants for the quenching of excited halogen atoms are due to resonant energy transfer processes and not to the paramagnetic nature of the quencher.     

Two-photon absorption spectroscopy of iodine monochloride in the 5 eV region

Two-photon high resolution sequential spectroscopy has been used to excite iodine monochloride from X¹Σ⁺ ground state to the intermediate A³Π₁ state and thence to a final electronic state at 4.82 eV. Vibrational and rotational analyses of this state have been carried out for both isotopic species. For I³⁵Cl, T_e = 38916.0 cm^?1 ω_e = 168.99 cm^?1, ω_ex_e = 0.357 cm^?1 and B_e = 0.05685 cm^?1. The state probably has Ω = 1 in case (c) coupling approximation. It is also shown how to two-photon technique enables rotational line structure of the A ← X transition to be selectively excited for either isotopic species at a resolution of 500000, from an absorption mixture containing natural iodine monochloride plus its iodine dissociation product at equilibrium vapour pressure.     

Comparison of reactivity of Ar(3Po) and Ar(3P2) metastable states. Products of quenching by some halogen-containing compounds

Vacuum UV emission from the products of quenching ofAr(³P_o) and Ar(³P₂) by several reagents has been compared. The large differences suggest that Ar(³P_o) and Ar(³P₂) preferentially yield respectively the D($\text{1}\text{2}$) and B($\text{1}\text{2}$) excited states of ArBr^★ or ArCl^★, which show specific, but very different, predissociation patterns.     

Kinetic spectroscopy in the far vacuum ultraviolet. Part I: Detection of (2p5) 2P32,12 fluorine atoms using atomic resonance spectrometry in the wavelength range 95–98 nm

A new experimental system for atomic resonance spectrometry at λ < 105 nm in a discharge-flow system is described. The spectrum of a fluorine resonance lamp has been studied, and possible precursors for the 2p⁴ 3s excited F atoms formed are suggested. Ground state (2p⁵²P_{$\text{3}\text{2}$}) and J-excited ²P_{$\text{1}\text{2}$} F atoms have been detected for the first time in resonance absorption and fluorescence using the first resonance transitions with wavelengths between 95.2 and 97.8 nm. Preliminary measurements (using both ⁴P-²P and ²P-²P lines) of the variations with concentration of absorption intensity by ground state F ²P_{$\text{3}\text{2}$} and by J-excited F ²P_{$\text{1}\text{2}$} atoms are reported; F atom concentrations were measured using a titration method based on the rapid reaction, F + Cl₂ → FCl + Cl.     

Production of electronically excited iodine atoms I(5p52P12) by collisional release in molecular I2

The appearance rate of 1^* (5p⁵²P_{$\text{1}\text{2}$}) following laser photolysis of molecular I₂ 1.2 kT below the dissociation limit o the I₂ (B³ Π_ou+) state has been monitored by time-resolved atomic absorption as a function of I₂ pressure. Data were also taken with N₂ as an added gas. The results confirm the production of I^* from the B state by a collisional process and reveal an additional process by which I^* continues to appear for several hundred nanoseconds after the laser pulse even at N₂ pressures as high as 750 torr.     

Preparation and synthetic utility of fluorinated phosphonium salts,bisphosphonium salts and phosphoranium salts

The synthesis and mechanism of formation of phosphonium salts of the type [R₃$\text{P}\text{+}$CFXY]Z^? (where X = F, Cl, Br; Y = Br, Cl; Z = Br, Cl), $\text{bis}$-phosphonium salts of the type [R₃$\text{P}\text{+}$CF₂$\text{P}\text{+}$R₃]2Br^?, and phosphoranium salts of the type [R₃$\text{P}\text{+}$$\text{C}\text{?}$F$\text{P}\text{+}$R₃]X^? (X = Br, Cl) will be presented. The applicability of these substrates in the generation of useful nucleophilic or electrophilic synthetic intermediates will be discussed.     

The quenching of excited iodine atoms by oxygen molecules as studied by opto-acoustic spectroscopy

The opto-acoustic spectrum of I₂ in the presence of various quenching gases — NO, O₂, CH₃I, SO₂, C₃H_S, N₂, and He — has been studied. Of these, the I₂/O₂ spectrum is quite different due to the near-resonant energy transfer I(²P$\text{1}\text{2}$) + O₂(³Σ) → I(²P$\text{3}\text{2}$) + O₂(^IΔ), wherein the resistance of the O₂((^IΔ) species to collisional relaxation severely distorts the acoustic signal. The photochemical production of excited ²P$\text{1}\text{2}$ iodine atoms commences at wavelengths considerably longer than the dissociation limit of the I₂B? state.     

A study of the near infrared emission bands of the hydroperoxyl radical at medium resolution

Emissions of the hydroperoxyl radical HO₂ in the spectral range from 1.0 to 1.6 μm were studied at low and medium resolution. The resolved spectrum shows the expected parallel band structure for the vibrational ovetone transition ²A″ (200-000); in the case of the vibronic transitions ²A′, 000 → ²A″, 000 and ²A′, 001 → ²A″, 000, however, comparison of experimental and computer simulated spectra shows that there also occur intense subbands with ΔK = 0, in addition to the ordinary ΔK = ± 1 transitions. The cause for the break-down of the type-C selection rule is not well known. In the reaction system of ethylene with discharged oxygen vibronic bands could be observed originating from ²A′ levels up to at least ν′₃ = 6. The most probable excitation mechanism for these high vibronic levels is the chemiluminescent reaction HCO + O₂ (¹Δ_g) → HO₂(²A′, 00ν′₂) + CO. From the computer fits to the spectra of HO₂ and DO₂ at medium resolution the origins of the 000-000 bands and the fundamental frequencies $\text{ν}$_3′ of the excited ²A′ state could be determined; the values are $\text{ν}$_o(HO₂)=7028 ± 3 cm^?1, $\text{ν}$_o(DO₂)=7034 ± 8 cm^?, $\text{ν}$_3′(HO₂)=927 ± 10 cm^?, and $\text{ν}$_3′(DO₂)=940 ± 28 cm^?1.     

The polarised two-photon excitation spectrum of benzene monocrystals at 6 eV

The two-photon excitation spectrum of a benzene single crystal at 4.2 K has been recorded in the region of the second absorption system. The onset of two-photon absorption occurs near 46 500 cm^?1 (quoted as a two-photon frequency). The spectrum has the appearance of a forbidden transition in that the system begins with weak lines which become dominated by an intense continuum at higher energies. The two-photon cross section at 55 000 cm^?1 (the limit reached in this study) is about 200 times greater than at 47 490 cm^?1 although the peak of this strongly allowed system has not yet been reached. The fwhm of the bands near 47 000 cm^?1 is 280 cm^?1, the same as in the one-photon spectrum at these energies. The polarisation ratio is much the same over the entire energy range, and is consistent with the two-photon operators (xz, yz) or (zz). An analysis of all the data available from the one- and two-photon spectra suggests that the transition is ¹B_1u ← ¹A_1g in which the vibronic intensity is derived from the ¹E_1u state in the one-photon and ¹E_1g in the two-photon spectrum.     

State determination of atoms formed by dye-laser induced photodissociation of KI in the near UV

By means of a time of flight technique, using high temperature surface ionization, we have been able to measure the internal energy of atoms formed in the photodissociation of KI at wavelengths between 265 and 335 nm. At all wavelengths only ground state K(²S_{$\text{1}\text{2}$}) is formed. Between 265 and 295 nm iodine is solely formed in the excited I(²P_{$\text{1}\text{2}$}) state, above 305 nm only in the ground state I(²P_{$\text{3}\text{2}$}).     

Far-infrared laser magnetic resonance spectrum of SeD (X2Π32)

Far-infrared laser magnetic resonance (LMR) spectra of SeD have been detected at 513 μm using a formic acid laser, and assigned to Zeeman components of the J = $\text{3}\text{2}$ → $\text{5}\text{2}$ transition in the six isotopic forms ^{82,80,78,77,76,74}SeD. Analysis yields the following B_o constants (cm^?1): ⁸²SeD 3.96047, ⁸⁰SeD 3.96284, ⁷⁸SeD 3.96532, ⁷⁷SeD 3.96657, ⁷⁶SeD 3.96793 and ⁷⁴SeD 3.97066. These values, combined with B_o for ⁸⁰SeH from 5.6μm LMR, yield r_e = 0.14634 nm for SeD.     

Collisional energy transfer to methane by octupole coupliing

A linear molecule or one electron atom interacting with a tetrahedral molecule is considered. Formulae are presented for various rotationally averaged E → R and V → R first order transition probabilities arising from dipole-octupole (R^?5) and quadrupole-octupole (R^?6) coupling. Relatively large amounts of rotational energy can be transferred in first order (ΔJ ? 3). With CH₄ as the octupolar partner, energy transfer upto 350 cm^?1 at room temperature is shown to proceed very efficiently. For the 5²P_{$\text{3}\text{2}$} → 5²P_{$\text{1}\text{2}$} transition in Rb, σ_qu is calculated to be ? 28 A² in quite good agreement with experiment and using an independent value of the octupole moment of CH₄. Energy transfer above 350 cm^?1 becomes rapidly less efficient. Among V → R transfer processes in the 500–700 cm^?1 range, the long range mechanism is almost certainly not the dominant one in the relaxation of CO₂⁺ (010) by CH₄ (σ_calc ≈ 10^?3 σ_obs) but will be important in the relaxation of SO₂.     

Isotopic selectivity in the sensitized dissociation of SF5Cl and CF3I by multiphoton excitation of SF6

The dissociation of SF₅Cl and CF₃I sensitized by multiphoton excitation of SF₆ by a pulsed CO₂ laser has been studied versus pressure, laser fluence, inert gas and optical frequency. Isotopic effects have been observed between ³²SF₅Cl/³³SF₅Cl and between ¹³CF₃I/¹²CF₃I and selectivity factors as high as α^?1_{$\text{33}\text{32}$} = 1.57 or α_{$\text{13}\text{12}$} = 1.23 obtained.     

An electrical conductivity (EC) study of the thermal dissociation of [Co(NH3)6]X3 and [Co(en)3]X3 complexes

The thermal dissociation of the [Co(NH₃)₆]X₃ (X = Cl^?, Br^?, I^?, and NO^?₃), [Co(en)₃]X₃ (X = Cl^?, Br^?, I^?, NO^?₃, HSO^?₄ and $\text{1}\text{2}$ C₂O^2?₄), cis- [Co(en)₂Cl₂]Cl, and trans-[Co(en)₂ClBr]NO₃ complexes was investigated by an electrical conductivity (EC) technique. During the thermal dissociation reactions, liquid or semi-liquid phases are formed which cause large increases in the EC of the compound. The effect of concentration of the complex in a matrix medium as well as the composition of the matrix material on the EC curves were also determined.     

Infrared high temperature spectra of aluminium chloride and related species

Isothermal cells of nickel with diamon windows were used to study various melts and vapours by infrared emission, transmission and reflectance techniques in the 860 to 300 K range with an evacuable Fourier transform spectrometer.IR vapour spectra of AlX₃ (X = Cl, Br, I) and GaCl₃ in transmission and emission were measured between 700 and 50 cm^?1. A comparable signal/noise ratio between the transmission and emission spectra was obtained above 200 cm^?1, below 200 cm^?1 the transmission spectra had better quality. The dimer and monemer spectra were assigned in terms of $\text{D}$_2h and $\text{D}$_3h symmetry, respectively, and compared with earlier Raman and IR matrix isolation data.Emission spectra of chloroaluminates AlkAlCl₄ (Alk = Li, Na, K, Rb, Cs) were recorded as melts between 1500 and 50 cm^?1. Increasing distortion of the tetrahedral AlCl^?₄ ion in the series Cs<Rb<K<Na<Li was observed. Emission spectra of AlkAl₂Cl₇ (Alk = Li, Na, K, Cs) indicate $\text{D}$_3d symmetry for Al₂Cl^?₇ with a linear Al-Cl-Al bridge as proposed from earlier Raman data. As a demonstration of reflectance technique an IR spectrum of ZnAl₂Cl₈ at ambient temperature is presented.     

Ultraviolet emission of molecular chlorine

The UV emission of Cl₂ from a new valence-shell state having 0⁺_u symmetry (T_c ≈ 59774 cm^?1, r_c ≈ 3.0 Å) was observed by focusing ≈ 500 nm laser radiation to gaseous chlorine. Excitation was achieved by virtual two-photon absorption from the B ³Π_0⁺u state formed by single-photon absorption stepwisely. The emission spectra showed transitions to the ground state as well as to the repulsive grade estate dissociating to Cl²P) + Cl(²P) products.