Bath gas pressure

Fig. 14.1 (a) Red shift of Cr emission line peaks as a function of Ar bath gas pressure at 3,230 K. The three curves correspond to the three peaks of the triplet centred on 27,820 cm-1, (b) Corrected MBSL spectra (orange) and Cr emission from a hollow cathode lamp at low pressure (blue). Relative red shifts for each peak are indicated [11] (reprinted with permission from Annual Reviews)... 

At the higher pressures of other ion-molecule techniques, such as flowing afterglow or pulsed high-pressure mass spectrometry," both of which operate with a bath gas pressure of about 1 torr, collisions of such an excited intermediate with the bath gas occur on a nanosecond to microsecond time-scale, in competition with the unimolecular dissociation rate. For these techniques, ions that are the... 

Although the Lindemann theory predicts that the rate constant should be independent of bath gas pressure when [M] > k2, this is not the case at lower pressures. The expression for the unimolecular rate coefficient is... 

The experiments of Pagsberg et al.25 were performed at bath-gas pressures (M = SF6) of 10 - 1000 mbar. A strong pressure dependence of the apparent bimolecular rate constants was found in this pressure range. 

The rate constants of the above reactions strongly depend on the bath-gas pressure. Time-resolved IR absorption spectroscopy was used by Pagsberg et al.254 to study the formation kinetics of FN02, whereas, for comparison, the decay of N02 was monitored by UV spectroscopy at 298 K and 341 K. 

Once prepared in S q with well defined energy E, donor molecules will begin to collide with bath molecules B at a rate determined by the bath-gas pressure. A typical process of this type is the collision between a CgFg molecule with approximately 5 eV (40 000 cm or 460 kJ mol ) of internal vibrational energy and a CO2 molecule in its ground vibrationless state 00 0 to produce CO2 in the first asymmetric stretch vibrational level 00 1 [11, 12 and 13]. This collision results in the loss of approximately AE = 2349 cm of internal energy from the CgFg,... 

Data for the decay of the OH density for several pressures of C2H2 at a particular T and P are shown in Fig. 4, as well as the plot from which the rate constant for these conditions is determined. The scatter exhibited is in accord with our estimates of 10-20% run-to-run error. A series of such measurements was made for bath gas pressures ranging from 10 to 100 torr. Typical bath gas mixtures contained equal amounts of N2 and SF. The results are given in Fig. 5. As seen in the figure, there are two sets at T = 1070 50K and 1180 40K for which the results are... 

From the mathematical point of view, the dynamics of product formation in the reaction scheme (14.2) is characterized by two timescales (see below). Our attempt to identify a single reaction rate amounts to exploring the conditions under which one of these rates dominates the observed evolution. In the limit of fast thermal relaxation relative to the rate of product formation, it is the latter slow rate that dominates the observed process. In the opposite limit it is the excitation process A A2 that determines the rate. The latter is then dominated by the first of the reactions in (14.1)— accumulation of energy in A, and is proportional to the strength of the thermal interaction, for example, the bathing gas pressure. 

Although ion transmission guides and ion traps both use the same universal physical laws to achieve control over ion behavior, the ways in which the laws are used are different, as are the objectives. The guides do not retain ions to gain control over their velocities and are used simply to transmit both slow and fast ions over a very wide range of gas pressures. Ion traps retain ions over a relatively long period of time so as to adjust their kinetic energies and thereby improve mass resolution. The so-called bath gas is used at carefully controlled pressures. 

C05-0140. When a sealed bulb containing a gas is immersed in an ice bath, it has a gas pressure of 345 torr. When the same bulb is placed in an oven, the pressure of the gas rises to 745 torr. What is the temperature of the oven in Celsius ... 

Figure 6. Rate constant for the recombination of Cr(CO)4 with CO as a function of bath gas (helium) pressure. The various symbols correspond to data obtained...

The emission spectrum consists of a series of weak bands starting at about 220 nm and then growing into a continuum from about 240 to 400 nm, with a maximum at approximately 270 nm as shown in Figure 5. Halstead and Thrush estimated that =65% of the emission occurs from the B2 state, =15% from the 3B3, and =20% from a combination of the A2 and Bi states [24, 28, 29] with a rate constant of 2 X 1CT31 cm6 molec 2 s 1 using argon as the bath gas at 300 K [53], As with the reaction of SO + 03 discussed above, collisional coupling results in a radiative lifetime that is pressure dependent. 

Worked Example 7.11 Hydrogen gas is mixed with a nitrogen bath gas . The overall pressure is p. If the mole fraction of the hydrogen is expressed as 10 per cent, what is its activity ... 

Let us take the reaction (10) of OH with S02 as an example of a termolecular reaction of atmospheric interest and examine how its pressure dependence is established. It is common in kinetic studies to follow the decay of one reactant in an excess of the second reactant. In the case of reaction (10), the decay of OH is followed in the presence of excess SOz and the third body M, where M is an inert bath gas such as He,... 

In this problem we will consider the kinetics of this unimolecular isomerization reaction in a nitrogen bath gas at 1500 K, using several different theoretical treatments. The high-pressure Arrhenius coefficients for this reaction are A00 = 1 x 1014 s-1 and E0 = 45 kcal/mol. 

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