Comments to Atkins: Physical chemistry, 7th edition.

Transcription

1 Comments to Atkins: Physical chemistry, 7th edition. Chapter 16: p. 483, Eq. (16.1). The definition that the wave number is the inverse of the wave length should be used. That is much smarter. p Absorption spectroscopy is not usually done by swept nearly monochromatic light, on the contrary, broadband sources are normally used. p. 483, footnote. If stimulated emission is included in the definition of absorption as in the footnote, also scattering (Rayleigh + Raman) should be included since they will also influence the net absorption measured. p. 484, fig. 16.1: The range of mid-ir is given in the text as cm -1, not cm -1 as in the figure. Change the figure. p. 484, line 8. Emission spectroscopy is not normally used in NIR or visible, but absorption. p. 485, line 7: to state that the sources in spectrometers are black-body sources is not correct, since they are usually not built as black-body sources with an equlibrium radiation distribution. An emitter not in thermal equilibrium with its surroundings is not a black-body source. p. 485, line 19 and 24: a W filament does decompose, it evaporates. p. 485, line 4-5 from bottom: The mechanism for the D 2 lamp described is wrong. p. 485, fig A double-beam configuration as in the figure is not the typical form today. Most applications are single-beam, take FT-IR as example. p. 485, fig The grating should not be mounted at the specular angle, thus zero-order with no dispersion. Wrong. p. 486, line 4: lasers can usually not be tuned over a range of frequencies. p. 486, fig The electron beam is moving several turns in the booster synchrotron, accelerating typically from 10 MeV to 500 MeV. This is not done in 20% of one turn, as in the figure. p. 486, fig Why is light scattered from the same points on the hills in the grating surface? The whole surface reflects. What is implied by this construction? p. 487, fig The grating is mounted for zero order scattering, which is wrong. One does not normally use orders 1 and -1 simultaneously, as implied in the figure. p. 487, eqs (16.4, 16.5). Dividing by ½ in both equations improves their form. However, it is even better to use a plain cosine function (deleting 1+) since then the average becomes zero. 1

2 p. 487, fig The interferogram should tend to zero at large values of p. That it becomes zero in this case at regular intervals is not a normal feature and should not be displayed. The right form (realistic form) of the interferogram is for example found by using the web calculator with frequencies 99, 100, 101 Hz. p. 488, fig : the angular range of the light from the sample is so large that it will not pass the monochromator. p. 488, line If light is scattered in the forward direction with no change in frequency, it is not scattered at all. Light scattered (thus in other directions) with no change in frequency is Rayleigh scattered. p. 488, line 28: The requirement of monochromaticity of the laser is modest, since most Raman shifts studies are quite large: using nm radiation (HeNe) gives a typical Stokes vibrational line at 700 nm (1500 cm -1 ). Thus, diode lasers can be used. p. 489, line 4 from bottom. MCT detectors are photoconductive, not photovoltaic. p. 494, line Spontaneous emission from rotation or vibration transitions can certainly not be ignored. For example, the spectrum on p. 482 is observed in emission. If this paragraph was correct, any fire would emit IR light mainly by stimulated emission, i.e. be a laser. p. 494, fig (b). There is no dipole formed by the transitions to the p orbital as shown, contrary to assertion. p Since the Doppler broadening is so small, it is not of interest to include it. The calculated width of 70 khz is much smaller than the displayed linewidth in the spectrum on p It is only 0.04 cm -1 in the middle IR, thus only measurable by interferometry (definitely not by FT-IR). p. 497, Fig All the moments of inertia are wrong: I c should be I a, I b should be I c, I a should be I b. p. 498, Table 16.1, line 1. The reduced mass µ is defined but not named for diatomic rotation, on p. 512 for diatomic vibration instead the name effective mass m eff is used, for the same quantity. p. 499, fig : Axes b and c should change place for the asymmetric rotor. p. 500, Fig The vertical axis is not in energy but wave numbers. p. 500 cont. It should be better to use ~ above all quantities in wave numbers, not just a few. p. 500, line component of angular momentum along any axis... (not about). p. 501, line 13: all the three axes of the molecule are the principal axes. The highest n symmetry axis should be called just that. 2

3 p. 501, fig (a): The molecule can not be kept in this position. J is constant in space while the molecule precesses around J. p. 502, fig : The molecules can not be rotating like this, its J vector precesses around the field direction. p. 504, fig : What happens if the spin of the incoming photon is in the reverse direction relative to the rotation of the molecule i.e. which would cause J= -1 according to this model? The molecule can obviously not go J --> J-1 in an absorption? Is the description not too simple? p. 506, Fig The form of the distribution is distorted in some strange way, not being thermal. Further, the lowest absorption line is much too small (it must be comparable in size to the others), and at the wrong distance from the frequency zero. p. 508, line 10: The unshifted Rayleigh radiation is not observed (only) in the forward direction, it is observed in all directions: otherwise it would not be Rayleigh scattered at all. p. 509, Fig The spaces between the band centre and the first lines in the branches are much too large and do not agree with the values given on the same page. p. 510, Fig The distances between the band centre and the first lines in the branches are much too large. The ratios of intesities are wrong, the lines closest to the laser line are J = 0 <-- 2 and J = 2 --> 0, thus from even J levels that should have lower intensity, not higher. p. 512, line 26. The reduced mass µ is defined but not named for diatomic rotation on p. 498, on p. 512 for diatomic vibration instead the name effective mass m eff is used, for the same quantity. p. 517, Fig The branch profiles are not correct, with the lines closest to the centre much too high. p. 518, line 14. Should be Fig p. 518, Fig The spacings around the band centre are much too large. p. 519, Fig The spacings around the band centre are much too large. p. 519, Fig The arrow is wrong if the band is anti-stokes. It should be pointed out that the figure is only correct for a Stokes band. p. 520, Fig The spacing is wrong from the centre of the band. p. 520, Fig The O and S branches are exchanged. Note that the scale is the Raman shift. 3

4 p. 525, line 8. A half-wave plate rotates the plane of polarisation, it is not a polarising filter. The signal at the detector will be almost constant under rotation of a half-wave plate since the detector is not sensitive to the state of polarisation.. Chapter 17 p. 546, Fig Axis indications are needed. Breaks in the arrows are needed to indicate that the rotational stacks are much smaller (factor 10 4 ) than the electronic transitions. p. 546, line 6. The d orbitals are not degenerate! See e g UPS results. p. 550, line 11 and Fig The fluorescence occurs within 10 ns after the exciting radiation starts, not after it extinguishes. p. 550, Fig Due to the long lifetime of the phosphorescence, the signal is much smaller at zero time than fluorescence, not of the same size. p. 550, Fig The potential energy curves indicate a diatomic molecule, probably studied in the gas phase, but the raditionless decay is typical for a condensed phase. More explicitness is required. p. 552, line 4. Since the potential energy surface is multidimensional, the point in the figure where the curves cross does not mean a common geometry. On the contrary, the shape of the molecule in the triplet state may be rather different than in the singlett state, even if this can not be shown in the arbitrary one-dimensional drawing. Note that this process probably refers to a large molecule, not to a diatom. p. 553, line 1. Same problem as just above, in p. 552, line 4. p. 554, line 26. intense flash of light is not in general correct, for example in a continuous wave laser, or in a laser pumped by an electric discharge where the pumping does not involve light. p. 554, line 29. The laser transitions should not be slow (meaningless phrase), the transitions with no laser action should be slow. p. 554, line 34. A is not unpopulated, it is in equilibrium with X. p. 554, Eq, (17.6). This statement is more confusing than informing: normally the number of modes is very large in the beam, and the condition in the equation is not correct. Due to the complex form of the cavity (stable, unstable etc.) this condition is meaningless. p. 555, Fig The lower panel only shows the deexcitation of the upper states, not the simultaneous absorption by the lower states, which is always there since the two Einstein coefficients involved are equally large (identical). This effect is the reason why a true population inversion is needed, not only a number of excited states. 4

5 p. 555, line There is nothing in the laser process itself that gives a low divergence beam. For example, the most common laser, the semiconductor laser, is constructed so that it gives a strongly divergent beam. It all depends on the geometry of the cavity. p. 556, line 20: wrong value, should be 3.0x10-8 s. p. 559, line 2-3 from bottom: rapid gas flow through the cavity is not commonly used. p. 560, line 7-8 in the legend of Fig Impossible to understand, probably wrong. Maybe it should be vibrational deexcitation? p. 561, Fig : how can the CO 2 molecule relax from v 3 = 3 and 2 down to v 3 = 1? If the energy is lost as radiation as it seems, the efficiency of this laser can hardly be as high as it is. p. 561, line 11: The lasing transition is normally forbidden. If it is allowed as stated, how can the laser work so efficiently? p. 561, line 3 from bottom: any wavelength is not true. p. 562, Fig This configuration is mainly used for CW lasers, not pumped by a flash lamp as stated in the text two lines down. Pulsed dye lasers do not use this jet construction. p. 567, Fig This layout is not so useful since the probe pulse can never come close to the pump pulse in time due to much longer beam path. Equal path lengths are needed to get the time zero and to measure directly after the pump pulse. p. 568, Eq. (17.9): v i should be used in the formula. 5