Chapter 18 Flashcards
18-1. What is a virtual state? A v s i a u e e s t l b t g s o t m a a e e s.
A v s i a u e e s t l b t g s o t m a a e e s. A virtual state is an unquantized electronic energy state that lies between the ground state of the molecule and an excited electronic state.
18-2. Why docs the ratio of anti-Stokes to Stokes intensities increase with sample temperature? S t a o a p i A-S s r i p o a e f a e v s i t g e s t a v s, i p i w t. T B d i m l t p t e v s o t e g s a h t.
S t a o a p i A-S s r i p o a e f a e v s i t g e s t a v s, i p i w t. T B d i m l t p t e v s o t e g s a h t. Since the absorption of a photon in Anti-Stokes scatte ring involves promotion of an electron from an excited vibrational state in the ground electronic state to a virtual state, it probability increases with temperature. The Boltzmann distribution is more likely to populate the excited vibrational states of the electronic ground state at higher temperatures
18-3. At what wavelengths in nanometers would the Stokes and anti-Stokes Raman lines for carbon tetrachloride (^ = 218, 314, 459, 762, and 790 cm- I) appear if the source were (a) a helium-neon laser (632.8 nm)? (b) an argon-ion laser (488,0 nm)?
The Raman spectra for CCl4 is composed of five bands at 218, 314, 459, 762 and 790 cm- 1 relative to the source radiation.
The Stokes spectrum will be at νex – νv and the anti - Stokes bands will be at νex + νv . Since a He - Ne laser excitation is at 632.8 nm (1/0.00006328 cm) or 15,654 cm- 1 , the Stokes bands will appear at 15, 872 (218), 15,968 (314), 16,113 (459), 16,416 (762) and 16,444 (790) cm-1 , the anti - Stokes lines are at 15,436 (218), 1 5,340 (314), 15,195 (459), 14, 892 (762) and 14,864 (790) cm- 1 .
These correspond to 630.0 nm, 626.3 nm, 620.6 nm, 609.2 nm, and 608.1 nm for the Stokes and 647.8 nm, 651.9 nm, 658.1 nm, 671.5 nm and 672.8 nm.
For the Ar - ion laser at 488 nm (20,492 cm- 1 ) the Stokes bands are at 20,710, 20,806, 20,951, 21,254, and 21,282 cm- 1 , or 482.6 nm, 408.6 nm, 477.3 nm, 470.5 nm, and 469.8 nm. The anti - Stokes bands are at 20,274, 20,178, 20,033, 19,730 and 19,702 cm- 1 , or 493.2 nm, 495.6 nm, 499.1 nm, 506.8 nm and 507.5 nm.
