Co-excited vibrations

Figure 5-20. Characteristic of forced vibration or resonance in rotating machinery. (Ehrich, F.F., Identification and Avoidance of Instabiiities and Seif-Excited Vibrations in Rotating Machinery, Adopted from ASME Paper 72-DE-21, Generai Eiectric Co., Aircraft Engine Group, Group Engineering Division, May 11, 1972.)...

Ex 35 Kcal/mole.15 We find that the CO product vibrational distribution calculated using the phase space model with Eav = 35-40 Kcal/mole is in good agreement with our experimental results (Figure 2). Thus, the measured CO vibrational distribution indicates that vibrational energy disposal to the photolysis products is determined at a point on the potential surface where the full reaction exoergicity is available. This suggests that the 351 nm excitation of W(CO)g results in the sequence of events, (2)-(4), where the asterisk denotes vibrational excitation. 

When formaldehyde is subjected to suitable optical excitation it dissociates into H2 and CO. The process is thought to involve an excitation to the first excited singlet state followed by internal conversion to a highly excited vibrational state of the ground singlet state that dissociates according to the equation... 

The guanine CO-stretch vibration is excited at three different pump frequencies with a spectrally narrow laser pulse (FWHM 12 cm 1). Transient-absorption spectra are measured using a systematically delayed, spectrally broad, probe pulse. A negative transient-absorption signal indicates a bleaching, whereas a positive signal reflects excited-state absorption. The overall decay of the signal is due to T relaxation. 

Let us consider the system XCO with the mass of the fictitious atom X, mx, changing continously from 1 (X = H) to 3 (X = T). The resulting term energies of the three relevant excited vibrational states are depicted as functions of mx in Fig. 13. For m = 1 the two stretching states (1, 0, 0) and (0, 1, 0) are well separated in energy and the assignment provides no problem. The variation of mx in principle does not affect the C-O stretching frequency and to2 would stay constant (in a diabatic sense). On the other hand, the X-CO frequency scales approximately as 1 A/mx and therefore... 

Sonobe and Rosenfeld (48,49) have measured the 4.7 pm infrared emission of CO. The extent of the CO vibrational excitation can be estimated using a cold gas filter containing CO and a 4.7 pm filter. If CO is vibrationally excited there is a smaller amount of attenuation of 4.7 pm fluorescence by the cold gas filter. When ketene is photolyzed at 193 nm, they estimate from their data that the rotational and vibrational temperatures are about 6700 and 3700 K, respectively. A high rotational temperature suggests that the C-C-0 angle is bent in the excited state. The CO vibrational excitation becomes less for longer excitation wavelengths. 

The reaction of CH2 with C02 was first postulated by Kistiakowsky and Sauer (13) as taking place via an a-lactone intermediate. The occurrence of this reaction was subsequently demonstrated by Milligan and Jacox (14) in low temperature matrices. These low temperature matrix isolation experiments, however, could not determine definitely the structure of the CH2 C02 intermediate. The result of our laser absorption experiment shows that the CO is vibrationally excited up to v — 4 with a distribution close to the one predicted by a statistical model assuming the existence of a long-lived CH2 C02 complex. This calculation, however, is insensitive to the structure of the complex assumed. Since the ground state triplet CH2 is known to be less reactive and kinetically behaves like CHj (15,16), which does not react readily with C02, the singlet A CH2 is assumed to be involved in the reaction. 

Rather than attempting to cool warm molecules one can try to synthesize cold molecules by associating cold atoms. The molecules thus formed are expected to maintain the translational temperature of the recombining atoms because the center-of-mass motion remains unchanged in the association process (save for the little. momentum imparted by the photon). This idea was first proposed by Julienne and j co-workers [343, 344] who envisioned a multistep association, first involving the continuum-to-bound excitation of translational continuum states of cold trapped. atoms to an excited vibrational level in an excited electronic molecular state. This step was followed by bound-bound spontaneous emission to the ground electronic state. (I... 

The vibrational state distribution for the ground state CaO product from the reaction Ca + C02 shows a similar monotonic decrease with increasing vibrational quantum number to that from Ca + 02 and, again, only 10% of the reaction energy appears as CaO internal excitation [383]. No information exists about the amount of CO excitation. There is also evidence that low-lying excited states of CaO are produced in the reaction which is again assumed to proceed via an electron-jump mechanism. 

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