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  1. Quantum Defect

    Does uranium monoxide exist?

    I guess I am with Borek. Lewis Electron Dot structures are a simplification for understanding the bonding in molecules. If you look at Lewis' original paper on the subject, he even proposes that the octet rule may have something to do with an atom being cubical, with electrons at the vertices...
  2. Quantum Defect

    UV Light Penetration Depth

    Beer's law combined with a larger absorbance at short wavelengths, compared with longer wavelengths.
  3. Quantum Defect

    Schools Surviving the First Year of College - Comments

    There is at least one typo: "... you are a year subscription to Physics Today..." I believe that one of the useful skills to begin to learn in the first year laboratory course is the ability to keep a good lab notebook. My first year physics lab instructor liked to give everyone a copy of a...
  4. Quantum Defect

    Types of hydrogen atom

    It helps to make these molecules with model kits. With your model of the molecule (or with one in your head), put dots of paint on two of the hydrogen atoms. If you can do some non-bond-breaking kind of motion to the molecule to take one form into the other [i.e. they are identical...
  5. Quantum Defect

    Infrared spectroscopy of water

    The first part of the counting the types of motion is the first part: 3 * N. This can be imagined as coming about by taking all possible combinations of the three cartesian directions on each atom. Imagine one possible motion has atom 1 move in the x direction, atom 2 move in the y direction...
  6. Quantum Defect

    Allowed/Forbidden Transition Dipole Moments

    The basic rule is: |<f|dipole operator|i>|2 < > 0 Where <f| is the final state, |i> is the initial state, and the dipole operator is sandwiched in between. Starting from this rule, you can use symmetry properties of the different kinds of rovibronic wavefunctions to come up with selection...
  7. Quantum Defect

    Questions on the Lyman Alpha Profile

    The second figure you link to shows a hydrogen spectrum where there is strong absorption at the line center. This is a single peak, where the top has been reduced in size due to the presence of cooler hydrogen between light source and observer. The depression at the center of the line makes...
  8. Quantum Defect

    Surface temperature of a planet revolving a sun

    You need to calculate the power incident on the planet from the sun. This can be approximated by the ratio of the cross sectional area presented to the sun (pi*r_planet^2) divided by the total area (solid angle) 4*pi*r_orbit^2 times the power output by the sun (assumes isotropic radiation). At...
  9. Quantum Defect

    Balmer Series

    We have all done things like this. :wink:
  10. Quantum Defect

    Adiabatic Cooling Help

    What is gamma? it should be the ratio of Cp/Cv, correct? Which is larger, Cp or Cv ? Should gamma be greater or less than one?
  11. Quantum Defect

    Balmer Series

    The sixth line means the sixth observed line. Here are the transisitons: n_i --> n_f 3--> 2 (first line) 4--> 2 (second line) 5--> 2 (third line) .... Which is the sixth line?
  12. Quantum Defect

    Questions on the Lyman Alpha Profile

    (1) Should be lots of measurements of the line. These measurements will be part of a bigger picture, though, like the article you link to -- they are using the line to infer other information. c.f. which comes from...
  13. Quantum Defect

    Molecular solids

    It might help if you give us (and yourself) some examples of molecular solids. With these examples, think about what kinds of forces/bonding exist between the individual units.
  14. Quantum Defect

    Effect of intermolecular hydrogen bonding

    What you are looking at is probably a list of periodic trends for the oxygen family hydrides (H2O, H2S, H2Se, etc...) As you move up the column, the boiling points decrease. H2S is a gas at room temperature, you would predict (based upon the trend) that H2O would also be a gas, and have an...
  15. Quantum Defect

    A question for helium energy transition

    Whoops. You are correct, I mistook the 3p-2s for the one you were asking about. Here is a better source: This source lists the transition (#73 in the list for He, on page 618) as being 1,344 cm^-1 -- in the infrared region.
  16. Quantum Defect

    What is your experience with caffeine?

    I had friends as undergrads who would drink Jolt Cola to stay up late. Some took NoDoz. I was able to stay up late without caffeine, even in my most sleepless semesters, where I would average five hours of sleep a night. I didn't start drinking coffee until graduate school, where I drank...
  17. Quantum Defect

    A question for helium energy transition

    I think that it should be allowed. The chart is showing observed lines. What wavelength/frequency would the 1s3p-1s3s transition be? It may be that the chart is showing prominenet lines in a particular wavelength region. The one you are looking for might lie outside of this window. This...
  18. Quantum Defect

    Why does collision frequency decrease with increasing T?

    Z = 2^(1/2) Na * c_bar * sigma / Vm c_bar = c1*T^(1/2) , Vm = c2 * T (constant p) Z = c3 * T^(1/2)/ T = c3 * T^(-1/2), where c1, c2, and c3 are constants. If Vm is a constant, then Z = c4 * T^(1/2)
  19. Quantum Defect

    Why does collision frequency decrease with increasing T?

    P/RT on the right is the same thing as 1/Vm, where Vm is the molar volume. What you have is essentially a volume swept out per second ( c * sigma) divided by the molar volume. The collision cross section has some small temperature dependence, but you can assume that it is a constant. c is...
  20. Quantum Defect

    Question about resonance energy

    The "resonance energy" is a bit of a misnomer in the case of CO2. Sure, you have resonance structures with different kinds of mulitple bonds (triple-single <--> double-double <--> single-triple), but most of the energy lowering is due to the fact that the pi electrons are in orbitals...
  21. Quantum Defect

    Moving to Washington D.C.! Tell me where to live!

    The Washington Metropolitan Area Transit Authority has a trip planner that is fairly useful for timing trips on public transport. It will do address to address plans. If you know where you will be working, you can "time" the morning and evening commute to various possible...
  22. Quantum Defect

    "Water circuit" equivalents of basic electric components

    But a "Weber" is a barbecue grill? I guess if you used too much lighter fluid, you could have some reasonable fear of death ... ... and is it a "fear of (death seconds)" or a "(fear of death) seconds" ... ? My favorite "analogy" of all time was in a quantum mechanics class taught by an...
  23. Quantum Defect

    "Water circuit" equivalents of basic electric components

    A Battery is more like a water tower, I think. It just sits there with potential energy until you tap it. Water also leaks out of these over time, running down -- just like a battery.
  24. Quantum Defect

    Basic Linear Alegbra for Quantum Mechanics

    Which step is confusing you? You might try to think about the "bra" and "ket" as vectors that make sense to you, for example 2-D unit vectors I.e. |a> = column vector (1,0); <a| = row vector (1,0); |b> = column vector (0,1); <b| = row vector (0,1) Things like <a|a> = 1 = <b|b> -- you can...
  25. Quantum Defect

    Question about resonance energy

    Here are the steps that I would use in making the ladder of enthalpies: C(s) [+ O2 (g) ] --> C (g) [ + O2 (g) ] O=O (g) --> 2 O (g) (Use bond enthalpy O=O) C(s) + O2 (g) --> CO2 (g) CO2 (g) --> C (g) + 2 O (g) (2 x bond enthalpy C=O) The number you have for C=O is way too small (it...
  26. Quantum Defect

    Future options as a Physics teacher

    CU has a very strong program in this: I couldn't see what the pre-reqs were for people interested in entering the program.
  27. Quantum Defect

    Future options as a Physics teacher

    In times gone by, Community College teachers often had Masters degrees. These days, there are lots and lots of PhDs looking for jobs. The glut of PhDs means that Community Colleges are hiring more PhDs. Most other universities will only hire PhDs, as well. There may be some "typical" PhD...
  28. Quantum Defect

    Steel versus Zinc Chloride

    Don't know if it will work, but we used to use something called "Aquadag" to paint on a nice flat-black graphite coating. Somehwat surprisingly, you can buy it in little bottles via Amazon:
  29. Quantum Defect

    Question about resonance energy

    Try drawing an energy diagram, using the enthalpies. You have a number of different kinds of enthalpies here. The first two are bond dissociation enthalpies: C=O ----> C (g) + O (g) The gistof the problem is to compare the energies using bond dissociation enthalpies (approximate) and...
  30. Quantum Defect

    Analytical vs physical chemistry for nuclear engineering

    Analytical chemists are interested in quantitative measurements of chemical species in complicated mixtures. Physical chemists are interested in understanding chemical behavior using physical principles. I think it would depend upon what kind of nuclear engineering you would be doing, but I...