Laser-induced fluorescence spectrum of argon matrix-isolated dichlorocarbene

Dichlorocarbene has been prepared for spectral investigation by the matrix reaction of alkali metal atoms with carbon tetrachloride at high dilution in argon followed by condensation onto a copper wedge held at 15 K. When these samples were irradiated with laser lines of wavelengths between 5682 and 4545 Å, an intense red emission system peaking around 7000 Å was observed. The spectrum of this emission revealed at least five progressions in the ground state bending and stretching fundamentals. A revised value of the ground state bending mode for CCl₂ was obtained from higher-resolution spectra using more diluted samples and various laser exciting frequencies. Carbon-13 enriched samples confirm the assignments of the bands to progressions in the ground state bending and symmetric stretching modes of CCl₂.     

Metastable argon atoms under significant neutral depletion in helicon plasmas by laser-induced fluorescence

We study the spatial distribution of the metastable-state argon atoms in high density helicon plasmas by means of laser-induced fluorescence. It is observed that the neutral argon in metastable-state has an anomalous radial distribution in density; it has a caldera-like shape radially, which is rare in typical low-temperature plasmas such as inductively coupled plasmas wherein the density increases toward the discharge center, as previously reported. The formation of the distribution can be explained as it forms by the combined effects of significant neutral depletion in high plasma density, off-axis electron-density distribution, and increasing diffusive loss toward the wall. To establish the assertion with the underlying physics, we calculate a simple global model and obtain the neutral density distribution in metastable-state under various conditions. The calculated results qualitatively agree with the experimental results.     

超声射流冷却S2自由基激光诱导荧光激发谱

在超声射流条件下.采用SF6/Ar(～10%)混合气束脉冲直流放电方法产生S2自由基,观测了32S2自由基在30000～35500 cm-1波段的激光诱导荧光激发谱.通过对所观测到的40多个振动谱带的归属,确定其中28个谱带为s2自由基B3∑μ一X3∑-g跃迁的(v'=1-9,0),(v'=1-8,1),(v'=1-7,2)和(v'=2-5,3)四个谱带序列.通过对所获谱带的转动分析,得到更为丰富的S2自由基B3∑-μ-X3∑-g跃迁谱带的转动光谱常数和更为精确的B3∑-μ电子态的平衡分子常数:Te,щe,щXe,Be,ae和Re.另外,还测得所有观测到的谱带的寿命,进一步丰富了S2自由基学∑-μ-X2∑-g跃迁谱带的光谱信息.     

The laser-induced fluorescence spectrum of the 1,2,3-trifluorobenzene radical cation

Laser-induced fluorescence spectra of the radical cation of 1,2,3-trifluorobenzene have determined the origin of the electronic transition and the lifetime of the excited state in both the gas phase and solid Ne matrices. The gas phase spectrum shows relatively poorly resolved vibrational structure, as the lines seem to be badly broadened by rotational contours. The matrix spectra show extensive, well-resolved vibrational structure with small but noticeable matrix perturbations. The structure is also rather irregular and differs considerably between the ground and excited states. All of these observations are consistent with a considerable change in geometry between the two electronic states.     

水污染物的激光诱导荧光测定

简单介绍了激光诱导荧光（ＬＩＦ） 产生的机理。以３ 倍频Ｎｄ：ＹＡＧ 激光（ 波长３５５ｎｍ） 为激发源,研究了水中几种典型污染物的ＬＩＦ 谱。结果表明这些污染物可用ＬＩＦ 方法加以探测和鉴别。     

The infrared spectrum of InCl3 in solid argon

We report the infrared spectrum of InCl₃ in solid argon. The observed spectrum is consistent with a planar D_3h structure for this molecule.     

The near-ultraviolet spectrum of diacetylene trapped in solid argon at 9 K

The absorption spectra of normal and deuterated diacetylene trapped in solid argon at 9 K were investigated in the near-ultraviolet region between 2000 and 3000 Å. The vibrational structure observed at low temperature for the band system at 2448 Å, which was previously reported by Haink and Jungen in the gas phase, and identified as a ¹Δ_u ← X¹Σ_g⁺ transition, was analyzed. A comparison between the spectra for C₄H₂ and C₄D₂ suggests some revisions in the upper-state vibrational assignments. The possibility that the upper state assumes a C_2htrans configuration of ¹A_u symmetry is examined. The matrix spectra also appear to indicate that the absorption spectrum observed at 2576 Å in the gas phase and which has been assigned to a ¹Σ_u^? ← X¹Σ_g⁺ transition may not originate in the ground state of C₄H₂.     

The UV absorption spectrum of the phenyl radical isolated in solid argon

Phenyl radicals have been generated by photodecomposition of nitrosobenzene isolated in solid argon at 12 K. In this medium the origin of the first UV absorption band of nitrosobenzene corresponding to theS ₀ S ₂ transition is found at 30260 cm^–1. Excitation with an excess energy of 2200 cm^–1 results in very efficient photodissociation. The fragments NO and phenyl are stable for many hours. Annealing of the sample above 35 K led to partial recombination and recovery of the absorption spectrum of nitrosobenzene. The UV spectrum of the phenyl radical was obtained in the wavenumber range 25000–45000 cm^–1, apparently without contamination by other species. It shows sharp lines at 25220, 33880, and 34820 cm^–1 and two broader maxima at 38360 and 41060 cm^–1. Of these only the line at 34820 cm^–1 had been assigned to the phenyl radical in earlier work. These data are compared to recent molecular orbital calculations.Dedicated to Prof. F. P. Schäfer on the occasion of his 65th birthday.     

Gas phase electronic spectrum of the HSCCS radical by laser-induced fluorescence spectroscopy

In a discharged supersonic jet of a CS₂ and C₂H₂ mixture, a vibronic band system of a new radical species was observed in the energy region 21 800-23 000 cm⁻¹ by laser-induced fluorescence (LIF) spectroscopy. The LIF excitation spectrum shows progressions with 490 and 80 cm⁻¹ separations. The vibronic structure of a dispersed fluorescence (DF) spectrum, obtained by tuning a probe laser to the vibronic origin band, also consists of progressions with 520 and 100 cm⁻¹ separations. A high-resolution laser scan provided a rotationally resolved LIF excitation spectrum for the vibronic origin band, showing the rotational structure of a-type transitions of a near-prolate top. Several chemical tests indicate that the spectral carrier contains sulfur atom(s), one hydrogen atom and more than one carbon atoms. Electronic transition energy, vibrational frequencies, and rotational constants of this species are similar to those of SCCS⁻ [M. Nakajima, Y. Yoneda, Y. Sumiyoshi, T. Nagata, Y. Endo, J. Chem. Phys. 119(2003)7805-7813.], and the spectral carrier was assigned as an isoelectronic radical, bent HSCCS. Ab initio geometrical optimizations supported the spectral carrier to be HSCCS. The observed electronic transition was assigned to be the transition, which corresponds to the Π-Π transition in the limit of linear geometry. The observed vibrations in the excitation and DF spectra were assigned as the symmetric CS stretching (ν₅) and SCC bending (ν₇) modes by comparing the results of theoretical calculations.     

Vibration-rotation spectrum of HCF (X̃1A′) by laser-induced fluorescence

The vibration-rotation spectrum of the HCF molecule was observed by laser-induced fluorescence with an Ar⁺ laser. The laser line of 514.5 nm coincided with two rovibronic transitions, ^rR₁(9) and ^pQ₅(9) for $\text{A}\text{?}{}^1\text{A″(020)-}\text{X}\text{?}{}^1\text{A′(000)}$. The spectrum consisted of the progression of bending vibrational mode ν₂. The rotational lines were fully resolved for each of the vibronic bands. The analysis yielded the vibrational and rotational parameters for both the ground and the excited vibronic states. The rotational parameters of the $\text{X}\text{?}{}^1\text{A′}$ state were obtained for four vibrational levels [(0v₂0), v₂ = 0 – 3].     

Influence of the mineral component in biotissues affected by calcinosis on their laser-induced fluorescence spectrum

Laser-induced fluorescence (LIF) spectra of human cardiac-valve tissues affected by calcinosis and of macroscopic calcinosis formations produced from resected cardiac valves with such pathology were investigated by comparison with analogous spectra of bone and myocardial tissue of an animal, LIF was excited by an excimer laser with λ=248 nm. In the spectrum of macroscopic calcinosis formations, luminescence bands of the mineral component were separted from the band of protein tissues when these tissues were subjected to heat treatment at 700°C. The investigations have shown that the LIF spectrum of a calcified tissue contains fluorescence bands of tryptophan and fluorescence bands of the mineral component (hydroxylapatite). A change in the spectrum of tissues with pathological processes can be cause not only by a relative change in the concentration of collagen elastin, but also by the additional fluorescenced of the hydroxylapatite mineral that is absent in a healthy cardiac tissue. It was found that the change in the spectrum characterized by the ratio of the LIF intensity at λ=330 nm to the LIF intensity at λ=450 nm is sufficiently large. This makes it possible to use measurements of the relative intensity of fluorescence at these wavelengths to control the degree of calcination of cardiac tissue. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 846–849, November–December, 1999.     

Ag8 fluorescence in argon

The fluorescence of Ag8 in an argon matrix and in argon droplets is reported. This is the first unambiguous assignment of the fluorescence of a metal cluster larger than the tetramer, indicating that the excited state lifetime is longer than previously thought. It is discussed as a possible result of a matrix cage effect. The excitation spectrum is compared with two-photon-ionization measurements of Ag8 in helium droplets and to known absorption data. The agreement is excellent. We propose that the excited states relax rapidly through vibrational coupling to a long-lived state, from which the fluorescence occurs.     

Photoemission of solid argon

Photoemission yield spectra of solid argon using synchrotron radiation for excitation in the photon energy range 11.7–16 eV show peaks closely following the known excitonic transitions, further peaks at 11.96 and 13.1 eV and also give an indication for band-gap photoconductivity.     

激光烧蚀Cu靶产生等离子体紫外段发射光谱的研究

利用波长532nm,脉宽15ns的Nd:YAG 激光器作用于Cu靶上,研究了产生等离子体的紫外段（180 nm～300 nm）发射光谱。在局部热力学平衡条件下,采用Boltzmann图表法估算了等离子体的电子温度,得到了电子温度随时间和空间的变化,以及电子温度随激光能量密度的变化。结果显示,随着激光能量的变化,电子温度有一个极大值。随着时间的发展,电子温度先减小,而后增大,接着缓慢减小。随着距靶面距离的增加,电子温度呈下降趋势。     

激光烧蚀Cu靶产生等离子体紫外段发射光谱的研究

利用波长532nm,脉宽15ns的Nd:YAG 激光器作用于Cu靶上,研究了产生等离子体的紫外段（180 nm～300 nm）发射光谱。在局部热力学平衡条件下,采用Boltzmann图表法估算了等离子体的电子温度,得到了电子温度随时间和空间的变化,以及电子温度随激光能量密度的变化。结果显示,随着激光能量的变化,电子温度有一个极大值。随着时间的发展,电子温度先减小,而后增大,接着缓慢减小。随着距靶面距离的增加,电子温度呈下降趋势。     

Resonance absorption and fluorescence in argon

Absorption cross sections of argon for argon resonance radiation have been measured by several techniques. The apparent cross sections are small (0·1 to 1·6 × 10^-18 cm²) for resonance absorption and the values depend on the technique used for measurement. These observations are interpreted in terms of extensive reversal and broadening in the source. The excitation and quenching of resonance fluorescence was studied to provide information about the rates of the processes

The rate constants were estimated relative to k _r, the rate constant for radiation. Radiation imprisonment leads to a reduction of k _r from its natural value and observations of the decay of resonance fluorescence suggest that k _r ～ 1·5 × 10⁵ s^-1 in our system at [Ar] = 2 × 10¹⁷ atom cm^-3. Combining this value with the relative values for the quenching rate constants gives k ₁ < 1·5 × 10^-13, k ₁′(M = N₂) ～ 6 × 10^-12, k ₁′(M = NO) ～ 4 × 10^-10, in units of cm³ s^-1 molecule^-1.     

The effect of 3-body forces and anharmonicity on the phonon spectrum of solid argon

The phonon spectra of solidified argon have been computed by a phenomenological rigid-atom-model. This model, which takes the constituent atoms as rigid-hard spheres, assumes that the potential energy of the solid is the sum of central and non-central interactions, and derives the same from the Buckingham-Corner potential function together with the Axilrod-Teller interaction term. The zero-point quantum and anharmonic effects, have been included. The effect of many-body forces as well as anharmonicity on the frequency spectrum and the lattice heat capacities of the solid is seen to be appreciable. The agreement between theoretical and the experimental results is not very satisfactory.     

Energy bands of solid argon

The band structure of solid argon has been calculated using a classical, non-relativistic, nonselfconsistent APW method. The crystal potential was constructed by a superposition of atomic potentials due to the neighbouring atoms. We used Slater's statistical exchange potential approximation. Our results have generally confirmed those by Mattheiss. Our calculation is extended however to include a wider energy region and other symmetry directions than those carried out by Mattheiss.