Pulsed molecular beam

Scherer J J, Paul J B, O Keefe A and Saykally R J 1997 Cavity ringdown laser absorption spectroscopy history, development, and application to pulsed molecular beams Chem. Rev. 97 25-51... 

Scherer, J.J. et al.. Cavity ringdown laser absorption spectroscopy History, development and applications to pulsed molecular beams, Chem. Rev., 97, 25, 1997. 

One of the gas mixtures was used in a pulsed molecular beam experiment. The result of the experiment is shown below. Which of the two gas samples, A or B, was used for this experiment ... 

The pulsed molecular beam cluster source has produced clusters of virtually every material—we have made clusters of even the most refractory transition metals, of group IIIB and IVB elements, and numerous oxides, carbides, and intermetallic alloys of these elements. 

The apparatus consists of a pulsed molecular beam, a pulsed ultraviolet (UV) photolysis laser beam, a pulsed vacuum ultraviolet (VUV) probe laser beam, a mass spectrometer, and a two-dimensional ion detector. The schematic diagram is shown in Fig. 1. 

Scherer, J. J., J. B. Paul, A. O Keefe, and R. J. Saykally, Cavity Ringdown Laser Absorption Spectroscopy History, Development, and Application to Pulsed Molecular Beams, Chem. Rev., 97, 25-51 (1997). 

When a pulsed molecular beam is used with a pulsed laser beam, the velocity of the photofragments can be obtained from the delay time between... 

Previous workers had used the molecular beam TOF technique (134) and the VUV flash photolysis LIF technique (135). Ling and Wilson (136) had suggested that either the A(2n) state of CN is produced in the original photolysis process or that I atoms were produced in the Pi/2 and 3/2 states. It had been previously shown (135), by collisional quenching studies, that the A state of CN was not produced. This earlier work has been reviewed by Baronvaski (137) but recently both he and others have done further work on this molecule using excimer laser sources in both static gases and pulsed molecular beams. 

Wittig and his co-workers (138) have studied the photolysis at 266, 320, and 355 nm in a static gas cell as well as in a pulsed molecular beam. At each of these wavelengths they report only on the CN(x2 +, v"= 0) radical product. 

Several groups (138,144,152-154) have reported on LIF studies of CN following the photolysis of BrCN in the A continuum at 193 nm and longer wavelengths. These studies have been done in a pulsed molecular beam as well as in a static gas cell. A symmary of the results of these studies is given in Table 6. 

Other than the earlier work reviewed by Ashfold et al. (3), only three studies on the photodissociation dynamics have been reported for this molecule (153,154,158). The first study reported the quantum state distribution of the CN radical obtained in an effusive molecular beam and in a static gas cell, while the second study reported the observations in a pulsed molecular beam. The dynamics remains the same despite the fact that the initial internal state distribution of the C1CN molecule changes. This of course shows that hot bands are not important in the photodissociation of this molecule at this wavelength. 

In the pulsed molecular beam studies, the results were used to calculate an impact parameter for the photodissociation process. From these impact parameters it was concluded that the recoiling CN fragment did not take the lowest energy path when it was departing from the halogen atom. Rather, because of strong impulsive motion, the trajectory that the CN rsdical... 

In a recent series of papers C. Wittig and his group have reported on the photolysis of NCNO in its first absorption band (540 - 900 nm). These experiments have been done both in a static gas cell (165) and in a pulsed molecular beam (166). 

The LIF studies of Hawkins and Houston were done in a static gas cell and with a pulsed molecular beam. Even though there is almost 20,000 cm-l of available energy, very little rotational excitation is observed. The rotational temperatures that were observed under both experimental conditions are summarized in Table 11. 

Figure 6-1. Schematic of pulsed molecular beam reflectron time-of-flight mass spectrometer.

The last important parameter to be determined is the desorption energy. It can be determined in an accurate way using a pulsed molecular beam [44]. At sufficiently low coverage to have a constant desorption energy, the desorption signal (in the second half period) decreases exponentially as a function of time, with a time constant that is the life time of the adsorbed molecule that depends on the temperature and on the desorption energy ... 

Figure 18 CO2 transients on 4nm Pd particles supported on MgO(l 00) as a function of sample temperature with an isotropic pressure of oxygen (5 x 10 8 Torr) and a pulsed molecular beam of CO (3.4 x 107 Torr equivalent pressure) (from Ref. [146]).

Volumetric measurements at room temperature showed that by far the greater part of the adsorption of carbon monoxide on Au/TiC>2 occurred on the support it followed the Langmuir equation and most of it was removable by pumping.23,83 About one-third of the titania surface was able to retain it, but there was little uptake on Au/SiC>2. Use of the double-isotherm method with Au/MgO showed that adsorption onto the metal was complete at about 1 atm, but on various samples the coverage never rose above 18%. On model Au/MgO(100) the maximum coverage attained using a pulsed molecular beam at room temperature was < 10%.54... 

III Pulsed Molecular Beam, Fourier Transform Microwave Spectroscopy 89... 

Linear hydrocarbon radicals have been the subject of intensive laboratory spectroscopic and radio-astronomical research since the early 1980s. In recent years, a considerable number of rotational spectroscopic studies of medium to longer hydrocarbon chains such as C5H, CeH, CgH, and ChH have been carried out using a pulsed molecular beam FTMW spectrometer. The high resolution offered by such a spectrometer allowed the detection of the hyperfine sphtting of rotational transitions. These measurements improved fine and hyperfine coupling constants and provided rest frequencies with accuracies better than 0.30 km s in equivalent radial velocity up to 50 GHz. Indeed, some of the small C H radicals with n < 9 have subsequently been detected in space, in molecular cloud cores, and in certain circumstellar shells. These hydrocarbon chains are among the most abundant reactive space molecules known. 

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