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.     

Theory of polarized fluorescence of polyatomic radicals upon photodissociation of complex molecules in the gas phase

The effect of rotational predissociation on the polarization response of an ensemble of photofragments is investigated within the framework of the model with free scatter of fragments for the most general case when both original molecules and fragments are asymmetric rotators. Photoinduced decomposition reactions with single- and two-photon excitation of fragment fluorescence are analyzed. Second- and third-order orientational correlation functions determining the polarization degree of fragment fluorescence are calculated. The behavior of these correlation functions depending on the shape of original molecules and fragments, directions of dipole moments, and characteristic times of the process are analyzed. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 908–914, November–December, 1998.     

Iodine photodissociation laser with thermal gas flow

The sealed-off repetitive iodine laser with a thermal gas flow recirculation is described. Experimental results concerning the studies of the laser fuel flow velocity and output pulse energy are presented. With the repetition frequency of 1 Hz the output energy 450 ml was achieved.Paper presented at the Workshop on Iodine Photodissociation Lasers, Bechyn 1986, Czechoslovakia.We want to thank Dr. J. Musil from Institute of Physics for much valuable advice and support of the program.     

Role of the gouy phase in the coherent phase control of the photoionization and photodissociation of vinyl chloride

We demonstrate theoretically and experimentally that the Gouy phase of a focused laser beam may be used to control the photoinduced reactions of a polyatomic molecule. Quantum mechanical interference between one- and three-photon excitation of vinyl chloride produces a small phase lag between the dissociation and ionization channels on the axis of the molecular beam. Away from the axis, the Gouy phase introduces a much larger phase lag that agrees quantitatively with theory without any adjustable parameters.     

Gas phase A-band short time photodissociation dynamics of trans and gauche conformations of 1-iodopropane and comparison with the solution phase short time photodissociation dynamics

A-band resonance Raman spectra are reported for gas phase 1-iodopropane. The gas phase absorption spectrum and resonance Raman intensities were simulated using time-dependent wavepacket calculations and a simple model in order to extract the A-band short time photo-dissociation dynamics for the trans and gauche conformers of 1-iodopropane. The gas phase short time dynamics for trans and gauche are very similar to the results obtained from a reanalysis of corresponding solution phase spectra. This indicates that solvation has little effect on the A-band short time photodissociation dynamics. However, the electronic dephasing parameters for the gauche conformer increase significantly upon solvation while the trans conformer parameters are almost the same in the gas and solution phases. This suggests that the gauche conformer in the A-band excited electronic state undergoes stronger interaction with the solvent than the trans conformer to give rise to faster electronic dephasing upon solvation for the gauche conformer.     

Two-dimensional NMR correlation experiments in the gas phase

The application of common two-dimensional NMR correlation experiments to gaseous analytes for structural elucidation is reported. Standard sequences such as COSY, HSQC, and HMBC are readily applied to volatile hydrocarbons and fluorocarbons. In experiments using (19)F or (13)C as the observed nucleus, it is possible to take advantage of efficient spin-rotation relaxation to perform common experiments swiftly (a (19)F COSY acquired in 6s is shown) or to render insensitive experiments possible on a practical timescale (e.g. a gas phase INADEQUATE at natural isotopic abundance in 14h). NOE-based experiments were not successful on the gaseous systems studied.     

On the deconfinement phase transition in the resonance gas

We obtain the constraints on the governing parameters of the dense hadronic gas model at the critical temperature and propose quasiuniversal ratios of the thermodynamic quantities. The possible appearance of thermodynamic instability is discussed. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 7, 487–491 (10 April 1996) Alexander von Humboldt Fellow. Published in English in the original Russian journal. Edited by Steve Torstveit.     

Spin relaxation of muonated radicals in the gas phase

We report on recent results obtained for longitudinal field (T ₁) spin relaxation of the muonium-substituted (muonated) free radicals MuCO, MuC₂F₄, MuC₂H₃F, and MuC₄H₈ (t-butyl), comparing with results reported earlier for MuC₂H₄ (and MuC₂D₄). Some comparison with transverse field (T ₂) data is also given. These data are fit to a phenomenological model based on NMR theory of spin relaxation in gases. The parameters of these fits are presented and discussed.     

Delayed luminescence of indole derivatives in the gas phase

Spectral and kinetic characteristics of delayed luminescence of indole derivatives in the gas phase have been studied. The mechanism for delayed luminescence has been shown to depend on the disposition of the two lowest excited singlet ππ*-states, ¹L_a and ¹L_b. For vapors of 3-methyl-and 2,3-dimethylindole having a small ¹L_a-²L_b energy gap ΔE (ΔE < 500 cm⁻¹), prolonged light emissions with maxima at 525 and 540 nm, respectively, have been observed and interpreted as luminescence of free radicals formed due to dissociation of an N-H bond. For vapors of 5-methoxyindole having ΔE ≈ 3700 cm⁻¹, annihilation of delayed luminescence has been observed. The lifetimes for triplet states of 3-methyl-, 2,3-dimethyl-, and 5-methoxyindole at T = 373 K equal to 30, 26, and 65 μsec, respectively, were calculated from the kinetics of the delayed luminescence. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 503–508, July–August, 2008.     

Atomic mercury photodissociation laser in the visible

Stimulated emission on two new pulsed laser lines in atomic mercury is reported. The laser emits at 435.8 and 546.1 nm, corresponding to the transitions 7 ³S₁ → 6 ³P₁ and 7 ³S₁ → 6 ³P₀ of the neutral atomic mercury atom. Population inversion is generated by photodissociation of HgI₂ vapor with a KrF laser at 248 nm. 150mJ of KrF laser radiation were focused into the HgI₂ cell by means of a cylindrical lens in a transverse pumping configuration. With a single end mirror pulses with a peak power of 3 kW and duration of approximately 1 ns were generated. The pumping mechanism is proposed to be a sequential three-photon process.     

Correlations in the Kosterlitz-Thouless phase of the two-dimensional Coulomb gas

The particle and charge correlations of the two-dimensional Coulomb gas are studied in the dielectric phase. A term-by-term analysis of the low-fugacity expansions suggests that the large-distance behaviors of the particle correlations are governed by multipolar interactions, similar to what happens in a system of permanent dipoles. These behaviors are compatible with the asymptotic structure of the BGY hierarchy equations; on the other hand, a new identity for the dielectric constant is used to show that the four-particle correlations decay as the dipole-dipole potential 1/r² when two neutral pairs are separated by a large distancer. Near the zero-density critical point of the Kosterlitz-Thouless transition, we resum the low-fugacity expansions of both 1/ and the charge correlation C(r). We thus retrieve the coupling constant flow equations of the renormalization group as well as the effective interaction energy of the iterated mean-field theory by Kosterlitz and Thouless. The coupling constant at the RG fixed point is then identified with 1/. The nonanalyticity of 1/ at the transition turns out to coincide with the divergence of the low-fugacity series for this quantity. The leading term in the large-distance behavior of C(r) is found to be the same as for external charges. Moreover, we exhibit the subleading terms which also contribute to 1/.     

Laser induced phosphorescence in gas phase thiophosgene

Luminescence is observed from gas phase thiophosgene on excitation with the 5287 Å line of an Ar⁺ laser. Analysis of the emission spectrum shows that the emitting level is the one initially populated by laser excitation of the $\text{(π}{}^1\text{← n)}\text{a}\text{?}{}^3\text{A}{}_2\text{-}\text{X}\text{?}{}^1\text{A}{}_1\text{2}{}_0{}^1\text{3}{}_0{}^1\text{4}{}_0{}^6$ band. Using a tunable dye laser, an excitation spectrum near the origin of this triplet system is obtained and analyzed. It appears that the observed luminescence is resonance phosphorescence resulting from direct laser excitation into a vibronic level of predominant triplet character.     

Zpif's law in the liquid gas phase transition of nuclei

Zpif's law in the field of linguistics is tested in the nuclear disassembly within the framework of isospin dependent lattice gas model. It is found that the average cluster charge (or mass) of rank n in the charge (or mass) list shows exactly inversely to its rank, i.e., there exists Zpif's law, at the phase transition temperature. This novel criterion shall be helpful to search the nuclear liquid gas phase transition experimentally and theoretically. In addition, the finite size scaling of the effective phase transition temperature at which the Zpif's law appears is studied for several systems with different mass and the critical exponents of ν and β are tentatively extracted. Received: 2 June 1999 / Revised version: 8 October 1999