Gases atomic masses from

Figure 31. (a) Dissociation probability as a function of the initial kinetic energy for Hj/NiflOO). The solid curves are from the quantum calculation, and the circles and diamonds correspond to the quantum-weighted classical and quasiclassical approaches, respectively (b) same as (a) except the gas atom mass is 2 (c) same as (a) except the gas atom mass is 3 (d) same as (a) except the gas atom mass is 7. The plots are from Chiang and Jackson (1987). 

Calculate the density (in grams per cubic decimetre, gdm" ) of argon gas at STP. The relative atomic mass (from the periodic table) of argon is 39.95. Hence, 22.7dm (1 mol) of argon gas weighs 39.95g. 

The previous discussion has centered on how to obtain as much molecular mass and chemical structure information as possible from a given sample. However, there are many uses of mass spectrometry where precise isotope ratios are needed and total molecular mass information is unimportant. For accurate measurement of isotope ratio, the sample can be vaporized and then directed into a plasma torch. The sample can be a gas or a solution that is vaporized to form an aerosol, or it can be a solid that is vaporized to an aerosol by laser ablation. Whatever method is used to vaporize the sample, it is then swept into the flame of a plasma torch. Operating at temperatures of about 5000 K and containing large numbers of gas ions and electrons, the plasma completely fragments all substances into ionized atoms within a few milliseconds. The ionized atoms are then passed into a mass analyzer for measurement of their atomic mass and abundance of isotopes. Even intractable substances such as glass, ceramics, rock, and bone can be examined directly by this technique. 

The total collisional energy between an ion and a neutral gas atom can be calculated from Equation 49.2, in which m, m are the masses of the colliding neutral gas molecule and the ion, respectively. Elab is ths energy imparted to the ion, and Ecm is the collisional energy referred to the center-of-mass of the ion and molecule. 

The triatomic hydrogen molecule ion H3+ was first detected by J. J. Thomson in gas discharges and later fully characterized by mass spectrometry its relative atomic mass, 3.0235, clearly distinguishes it from HD (3.0219) and from tritium... 

Figure 5.19 Formation of amino acids on ice surfaces irradiated in the laboratory (Nature Nature 416, 403-406 (28 March 2002) doi 10.1038/416403a-permission granted). Data were obtained from analysis of the room temperature residue of photoprocessed interstellar medium ice analogue taken after 6 M HCl hydrolysis and derivatization (ECEE derivatives, Varian-Chrompack Chirasil-L-Val capillary column 12 m x 0.25 mm inner diameter, layer thickness 0.12 pirn splitless injection, 1.5 ml min-1 constant flow of He carrier gas oven temperature programmed for 3 min at 70°C, 5°C min-1, and 17.5 min at 180°C detection of total ion current with GC-MSD system Agilent 6890/5973). The inset shows the determination of alanine enantiomers in the above sample (Chirasil-L-Val 25 m, single ion monitoring for Ala-ECEE base peak at 116 a.m.u.). DAP, diaminopentanoic acid DAH, diaminohexanoic acid a.m.u., atomic mass units.

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