Infrared multiphoton dissociation of propynal: time resolved observation of CO (ν≥1) IR emission at 4.7 μm (original) (raw)
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Physics of laser action using high vibrational excitation of CO molecule
Proceedings of SPIE - The International Society for Optical Engineering
Revision of theoretical model of CO laser kinetics was performed including new data on intra-and intermolecular vibration exchange processes and vibration relaxation in highly excited CO molecules, spontaneous radiation Einstein coefficients for fundamental and overtone bands of CO molecules and cross sections for cascade excitation and deexcitation of CO molecules by electron impact.
The Journal of Chemical Physics, 2002
We report quantitative dissociation yields for the reaction CH 3 OH (v OH) → nh CH 3 ϩOH induced by infrared multiphoton excitation of methanol pre-excited to various levels of the OH stretching vibration (v OH ϭ0, 1, 3, 5). The yields are measured by detecting OH using laser induced fluorescence. It is demonstrated that for low levels of pre-excitation (v OH ϭ0, 1, 3) there is a substantial nonlinear intensity dependence, as a higher yield is found for self mode-locked CO 2 laser pulses ͑with higher peak intensity͒ as compared to single mode pulses of the same laser fluence, but lower peak intensity. In contrast, at high levels of preexcitation (v OH ϭ5) this nonlinear intensity dependence is absent. Quantitative model calculations are carried out using a case B/case C master equation approach that takes nonlinear intensity dependence into account. The calculations are consistent with the experimental results and confirm the prediction that an important part of the selectivity of the CO 2 laser excitation step in infrared laser assisted photofragment spectroscopy of CH 3 OH is due to this nonlinear intensity dependence. We discuss further consequences of these experimental observations and theoretical predictions, which are also extended to infrared multiphoton excitation of C 2 H 5 OH. Infrared ͑C-O͒ chromophore band strengths are reported for CH 3 OH and C 2 H 5 OH.
Chemical Physics, 1995
The time-resolved infrared fluorescence (IRF) technique has been used to study the vibrational deactivation of CO2(00°1) by large polyatomic molecules at ambient temperature (295 + 2 K). The excited CO 2 molecules were prepared by direct pumping with dae P(21) line of a pulsed CO 2 laser at 10.6 i~m. The bimolecular rate constant for deactivation by CO 2 was determined to be (0.353 + 0.026) × 103 Torr-~ s-1, in excellent agreement with previous work. The rate constants for deactivation by the large polyatomic molecules, s-1, respectively. Experimental deactivation probabilities and average energies removed per collision are calculated and compared. There is little difference in deactivation probabilities between the acyclic ririg compounds and their aromatic analogues but the perfluorinated compound, C6F 6 is clearly less efficient than its hydrocarbon analogue, C6H o. The perdeuterated species, C6D 6 and C7D 8 show considerably enhanced deactivation relative to the other species, probably as a result of near-resonant intermolecular V-V energy transfer. 0301-0104/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0301-0104(95)00257-X
The Journal of Chemical Physics, 1980
We have measured the vibrational (v), rotational (J,K), and translational energy, (ET), of the X̃ CF2 and X̃ CFCl fragments formed in the CO2 laser induced multiphoton dissociation of CF2CFCl (chlorotrifluoroethylene): CF2CFCl→CF2 (v,J,K)+CFCl(v,J,K)+ET(v,J,K), which was the only detectable reaction path for CF2CFCl. More vibrational energy (Ev) appears in CF2 than in CFCl. Direct spectroscopic measurements of populations in levels 0<ν2<7 show that Ev is distributed statistically in the bending mode (ν2) of CF2 according to P (Ev) =exp(−Ev/kTv), where P (Ev) is the probability of a CF2 product being formed with a particular amount of energy in ν2, and the vibrational temperature which characterizes the nascent distribution is Tv(ν2) =1860±250 °K. A vibrational relaxation method was used to accurately determine fo, the fraction of CF2 and CFCl molecules initially formed in the ground vibrational level. The measurements of fo showed that the energy in the stretching modes (ν1 an...
Journal of Physics D: Applied Physics, 2001
Studies of the vibration-vibration (VV) exchange in CO molecules excited up to vibration quantum numbers v = 20 have been performed both theoretically and experimentally. A new kinetic model which takes into account the multi-quantum VV exchange in the temperature range T = 100-300 K is described for the first time. A description is given of the experimental methodology allowing for studies of the effects of the relaxation of the vibrational distribution after a sudden disturbance. The disturbance of the vibrational distribution is produced by a Q-switched short pulse of single line radiation in fundamental band. The relaxation is studied by measuring the laser pulse energy of the second pulse initiated by resonator Q-switching produced with a variable time delay relative to the first pulse. A set of kinetic rate constants accepted in the model for various gas temperatures, vibration level numbers and number of exchanged vibration quanta from 1 to 4 is presented. The good agreement between the experimental data and the results of the advanced theory is the first direct evidence in support of the multi-quantum exchange model.
JETP Letters, 2010
1. The investigation of intramolecular vibrational energy redistribution (IVR) in molecules is one of the central items in molecular dynamics research . Interest in the investigation of IVR is primarily associ ated with the development of methods of laser initia tion and/or control of targeted photochemical reac tions. The prospect of implementing selective chemi cal processes in a bond (or a group of bonds) by the resonant excitation of a certain vibration in a molecule is of particular interest. One of the most efficient methods of vibrational excitation of molecules is based on the effect of their multiphoton excitation by reso nant infrared laser radiation (IR MPE). When a mol ecule is excited in this process above the dissociation threshold D 0 , it dissociates; i.e., infrared multiphoton dissociation (IR MPD) occurs (IR MPE and MPD were described in more detail in ). IR MPD is characterized by a high intermolecular (including iso topic) selectivity . At the same time, numerous experiments performed with micro and nanosecond laser pulses show that the intramolecular (including mode) selectivity of IR MPE is absent and the subse quent dissociation of molecules is statistical. This behavior is explained by the fact that IVR prevents the selective photochemical processes in the bond [1, 2]. The reason is that the energy accumulated in an indi vidual resonantly excited vibration above a certain threshold value E st (E st is the so called stochastization threshold, see, e.g., ) is redistributed over the other molecular vibrations until achieving equilibrium. This process leads to the loss of mode selectivity of excita tion and, finally, to the statistical character of the sub sequent reactions, in particular, the dissociation of molecules. The E st value for small (five to seven atomic) molecules is 4 to 7 × 10 3 cm -1 . It is also assumed that the characteristic time of IVR lies in the pico and subpicosecond ranges .
The infrared multiphoton photochemistry of methanol
The Journal of Chemical Physics, 1977
CO2 TEA laser has been used to initiate the multiphoton dissociation of CH3OH, both pure and with NO added as a free radical scavenger. The decomposition of CH3OH at the high power density of the focused laser radiation results in molecular and free radical initiated products. Decomposition through molecular intermediates appears to proceed via CH3OH+nhν→CH2O*+H2 and CH2O* →CO+H2, and comprises ∼90% of the consumed CH3OH in ∼3000 laser pulses. The radical initiated process CH3OH+nhν→CH3 +OH ultimately results in the stable products C2H4, C2H2, and CH4 to an extent of ∼10% of the CH3OH consumed. Luminescence from the focal zone is due to emission from OH†, CH†, C†2, and possibly CH2O†. Stable products as well as the visible luminescence due to the electronically excited diatomic radicals are followed as a function of pressure, time, and addition of the free radical scavenger gas NO. Both major photodecomposition routes appear to be non-Boltzmann.
Laser Chemistry, 1987
The vibrational relaxation mechanism of CH3F whose ν3 mode is excited by a transversely excited atmospheric (TEA)CO2 laser-pulse has been discussed on the basis of observation of the laser-induced fluorescence (LIF) of the ν3 overtones and of the C–H stretching modes and kinetic analyses. The time-evolved LIF in the 3-μm region was found to be dependent significantly on the laser fluence; at a low fluence (<0.01 J cm−2), the emission intensity increased almost exponentially with a rate similar to the one determined in the experiment with a Q-switched laser, while at a higher fluence…
Continuous-Wave Laser Action on Vibrational-Rotational Transitions of CO2
Physical Review
We have obtained cw laser action on a number of rotational transitions of the Z"+-Zg+ vibrational band of CO2 around 10.4 and 9.4p. The laser wavelengths are identified as the P-branch rotational transitions from P(12) to P(38) for the 00'1-10'0 band and from P(22) to P(34) for the 00'1-02'0 band. Strongest laser transition occurs at 10.6324' {vacuum). A cw power output of about 1 mW has been measured. All these laser transitions can also be made to oscillate under pulsed discharge conditions with a small increase in the peak laser power output. No E-branch transitions have been seen to oscillate either under cw or pulsed discharge conditions. The wavelength measurements are in reasonable agreement with earlier measurement of the bands in absorption, but there are slight differences. These are ascribed to possible pressure-dependent frequency shift eBects. A study has been made of the time dependence of the laser output under pulsed excitation, and some conclusions about possible excitation processes are given. Theoretical interpretation given earlier for laser action on vibrational-rotational transitions is discussed in a generalized form. The theory is applicable to both the linear polyatomic molecules and the diatomic molecules.