Saturation spectroscopy in molecular iodine by intermodulated fluorescence

The hyperfine structures of the P(13)R(15) (43−0) lines (5145Å) in molecular iodine were observed at very low pressures using a new saturated fluorescence technique. Two oppositely-directed beams from the same laser are chopped at different frequencies and the modulation of the fluorescence is monitored at the sum frequency.     

The hyperfine structure of molecular iodine in saturated fluorescence

The hyperfine structure of the R(127) 11-5 line (633 nm) of ¹²⁷I₂ were investigated by means of the saturated fluorescence excited in the resonator of a single mode ³He-²⁰Ne laser. Fourteen hyperfine components were detected in the tuning range of the laser at pressures from 15 to 240 mtorr.     

Fluorescence and fluorescence excitation spectra of jet-cooled carbazole

The fluorescence excitation spectra of jet-cooled carbazole molecules at vibrational temperatures of 55 and 80 K and the fluorescence spectrum of these molecules excited by radiation at the frequency of a pure electronic transition are measured. As the vibrational temperature increases, the excitation spectra exhibit a series of lines of the same symmetry, which are caused by the interaction of the active vibration with a subensemble of optically inactive vibrations. The final symmetry of the totally and nontotally symmetric vibrations is determined from the shape of the rotational contours of the lines of vibronic transitions. The values of a decrease in the frequency of the nontotally symmetric vibrations in the first excited electronic state S ₁ due to their interaction with the electronic state S ₂ are calculated to be up to 100 cm^?1. The frequencies of the pure electronic transitions in the absorption and fluorescence spectra coincide with each other and are equal to 30809 cm^?1, the frequencies of vibrations in the ground state S ₀ exceeding the frequencies of the corresponding vibrations in the excited state S ₁. The degree of polarization of the integral fluorescence is determined for a series of vibronic transitions of the a ₁ and b ₂ final symmetry that are observed in the fluorescence excitation spectra, and the contribution of the intensity with the borrowed polarization θ_⊥ to the integral fluorescence is calculated. It is found that the intensity θ_⊥ is higher for the transitions of the b ₂ symmetry and can reach ≈50%.     

Particular features of fluorescence of jet-cooled vapor of 2,3-diazabicyclooctene

The fluorescence and fluorescence excitation spectra of azocompound, 2,3-diazabicyclo[2.2.2]oct-2-ene, have been studied using jet cooling. The violation of the mirror symmetry between the fluorescence and fluorescence excitation spectra due to an intense long-wavelength emission that manifests itself in solutions and in the gas phase cannot be eliminated even by jet cooling. It has been revealed that the bands of pure electronic and vibronic transitions are split by 0.55 cm^?1, which is caused by tunneling with accompanying emission from an intermediate short-lived state and which may be the reason for the violation of the mirror symmetry of the spectra upon tunnel inversion.     

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.     

High resolution laser induced fluorescence excitation spectroscopy of jet-cooled terrylene

High resolution laser induced fluorescence excitation spectra upon absorption in the A¹B_3u ← X¹A_g band of jet-cooled terrylene have been recorded. Precise energies of three vibronic transitions are deduced. Low lying vibrations are found in both electronic states. Rotational constants in ground and excited state are determined by band contour analysis. Terrylene is a medium-size polycyclic aromatic hydrocarbon (PAH) and a possible carrier of diffuse interstellar bands (DIB). The results of the jet experiments are discussed regarding the PAH-DIB hypothesis.     

Polarized fluorescence of monoanions of Zn-octaethylphlorin

We investigate the luminescent properties (radiation spectrum, polarized spectrum) of the monoanions of Zn-octaethylphlorin, which is an intermediate product of the reduction, reaction of porphyrins. An oscillator model is presented that includes three electronic oscillators, with a long-wave one being oriented perpendicularly to the remaining two. The lifetime of the excited singlet state τ=30±15 nsec is estimated. Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 329–332, May–June, 1997.     

Polarized fluorescence spectroscopy of human tissues

We report the results of a study carried out to investigate the effect of blood absorption on polarized and unpolarized fluorescence from resected tissue samples and tissue phantoms. The signatures of blood absorption were found to be significantly smaller in polarized fluorescence than in unpolarized fluorescence spectra. The reduced effect of blood absorption on polarized fluorescence also leads to reduced site-to-site variability in polarized fluorescence intensity and line shape compared with unpolarized fluorescence.     

Quantitative measurement of naphthalene in low-pressure flames by jet-cooled laser-induced fluorescence

We have recently developed a new laser based set-up (Jet-Cooled Laser-Induced Fluorescence) for the analysis of aromatic compounds generated in flames. This method relies on the extraction of the species from the flame via a thin microprobe and their direct analysis inside a supersonic free jet by Laser-Induced Fluorescence (LIF). Under the supersonic conditions of the jet, the vibronic spectra of the molecules become structured as the possibility of electronic transitions is reduced, allowing their selective detection by LIF. In addition, due to the very low quenching efficiency inside the jet, LIF signals can be directly related to the population of the probed species and easily calibrated into absolute concentrations. All of the work presented here has been carried out for naphthalene, which is an important PAH involved in soot formation mechanisms. The calibration procedure is described in detail. We also report a detailed study of the quantitative features of the technique, in particular cooling efficiencies and collision rates as well as some additional potential factors that could bias the quantitative aspect of the method. Finally, the possibilities of the technique for the measurement of PAH within flames in the presence of soot particles along with its accuracy and reproducibility are demonstrated by recording naphthalene mole fractions profiles in several rich CH₄/O₂/N₂ flames. A detection limit of the order of a ppb is demonstrated under flame conditions with and without the presence of soot particles.     

Electron impact induced fluorescence of dissociating fragments from jet-cooled methane,methanol and ethanol

Dissociation fragments, following 20 keV electron impact on supersonic jet targets of methane, methanol and ethanol, have been analysed to determine rotational temperatures. The intensities of individual rotational lines of the CH A² Δ-X²Π, CH B²∑^- -X²Π and CH⁺A¹ Π-X¹∑⁺ transitions were measured and fitted to Boltzmann distributions. The temperatures obtained were about 4000 K for the CH A-X, 2000 K for the B-X and 1650 K for the CH⁺A-X transitions. The recorded spectra showed distributions at single temperatures. The intensities were also fitted to theoretical distributions in order to obtain excess energies. Possible fragmentation mechanisms are discussed.     

Laser induced fluorescence line narrowing in iodine

A complementary technique to Lamb dip absorption spectroscopy in gases is described which allows observation of homogeneous linewidths in fluorescence. Hyperline spectra of iodine excited by a single mode argon laser beam at 5145 Å are presented for the 43-13 and 43-11 bands at 5970 and 5830 Å respectively.     

Polarized fluorescence of radicals in photodissociation of disulfides in the gas phase

The polarization of the fluorescence of radicals formed in laser-induced photodissociation of some disulfides in the gas phase is measured. Experimental data obtained in the study are interpreted within the free recoil model. It is shown that polarization experiments carried out to investigate photodecay in vapors allow researchers to uniquely the intramolecular direction of the dipole moments of transitions with absorption and emission. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 54–59, January–February, 1999.     

Laser sounding of molecular iodine in the atmosphere

The lidar equation for the fluorescence of ¹²⁷I₂ molecules is numerically solved. All the radiation wavelengths of a copper vapor laser are considered with the aim of choosing the one that is the most appropriate for detection of the minimum possible concentration of iodine molecules when this laser is used as a radiation source of a fluorescence lidar.     

Spin-exchange-induced circularly polarized molecular fluorescence

We have measured the circular polarization of light emitted from both atomic H and molecular H2 after bombarding H2 with longitudinally polarized electrons. For both atomic and molecular fluorescence near threshold we observe a circular polarization as great as 10% of the electron polarization. This represents the first direct observation of spin transfer in electron-molecule collisions.     

Pressure-induced molecular dissociation in iodine at low temperatures

Abstract

Synchrotron x-ray diffraction experiments at low temperatures have revealed that even at 35K the molecular dissociation starts taking place at P_S=21.5 and finishes at P_f=26.1GPa. An extrapolation of the phase boundary thus obtained at several temperatures intersects the T=4K line at P_S=21.6 and P_f=26.3GPa. This result, inferring the monatomic structure to be realized at P=30GPa and T=4K, leads to a discrepancy against the recent Mössbauer result obtained at the same point in the P-T phase diagram.     

Highly efficient, resonant Raman molecular iodine laser

A highly efficient 1.3-microm molecular iodine Raman laser is demonstrated. Multiwavelength output powers of 600 mW and photon-conversion efficiencies of 78% are demonstrated for a 532-nm pump source. Single-wavelength output powers of 480 mW and photon-conversion efficiencies of 67% are also realized. A simple thermal lensing model is used to optimize the pump and Stokes mode sizes.