Lifetimes Of Rotational Levels Research Articles

Lifetime Measurements of the D1Π State of HfS and the b3Π 1 State of HfO

Lifetime measurements of individual rotational levels in excited states of hafnium oxide and hafnium sulfide have been performed using population probing by resonant two-photon ionization in a molecular beam. For the b 3Π 1 state of HfO rotational levels in the vibrational level v=0 were found to have lifetimes in the region 650–700 ns. For the D 1Π state of HfS rotational level lifetimes in the vibrational levels v=0 and v=1 were determined to be around 240 ns. The technique used here provides very accurate results and the uncertainty in the reported values is only about 2%. Possible sources of errors are examined. The absorption oscillator strengths from the ground state are calculated.

Rotational level lifetimes and self-quenching of 127I 2 by fluorescence demodulation spectroscopy

Fluorescence demodulation spectroscopy (FDS) has been applied to determine lifetimes and self-quenching cross sections of two absorption lines in the X-B spectrum of 127-iodine. The lines are the R(93), 2-16 ( v″- v') transition and the P(95), 1-14 ( v″- v') transition. Both states exhibit pure lifetimes of about 280 ns and cross sections for self-quenching of about 46 Å 2. Values of both the lifetimes and the cross sections are considerably smaller than previously reported.

Radiative lifetimes of CH2(b 1B1)

Radiative lifetimes are reported for CH2(b 1B1) in a wide range of rotational states in the (0,14,0), (0,15,0), (0,16,0), and (0,17,0) vibrational levels. Laser photolysis of ketene in a supersonic-jet expansion produced CH2(a 1A1) which was excited to single rovibrational levels of the (b 1B1) state by a second laser. Analysis of the temporal evolution of the fluorescence (b 1B1)–(a 1A1) yielded collision-free radiative lifetimes for the (b 1B1) state. The measured lifetimes range from about 4 to 10 μs and decrease with increasing vibrational energy. For the (0,14,0) overtone, the lifetimes increase slightly as a function of J (Ka=0). However, the lifetimes of rotational levels with Ka=0 in the (0,16,0) vibrational state are found to be independent of the rotational state. Calculations of the vibronic lifetimes show that the considerable lifetime lengthening when Ka≥1 is due to Renner–Teller coupling to the ã 1A1 state. The random lifetime fluctuation observed in some vibronic bands is probably due to spin–orbit coupling to the X̃ 3B1 state, e.g., 413 and 414 of (0,15,0). Here the radiative lifetime of the singlet component is shorter than that of the corresponding triplet component.

ChemInform Abstract: ISOTOPE, ELECTRIC FIELD, AND VIBRATIONAL STATE DEPENDENCE OF SINGLE ROTATIONAL LEVEL LIFETIMES OF S1 FORMALDEHYDE

Chemischer InformationsdienstVolume 11, Issue 38 Physical Organic Chemistry ChemInform Abstract: ISOTOPE, ELECTRIC FIELD, AND VIBRATIONAL STATE DEPENDENCE OF SINGLE ROTATIONAL LEVEL LIFETIMES OF S1 FORMALDEHYDE J. C. WEISSHAAR, J. C. WEISSHAARSearch for more papers by this authorC. B. MOORE, C. B. MOORESearch for more papers by this author J. C. WEISSHAAR, J. C. WEISSHAARSearch for more papers by this authorC. B. MOORE, C. B. MOORESearch for more papers by this author First published: September 23, 1980 https://doi.org/10.1002/chin.198038050AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume11, Issue38September 23, 1980 RelatedInformation

Isotope, electric field, and vibrational state dependence of single rotational level lifetimes of S1 formaldehyde

Additional single rovibronic level lifetimes of S1 H2CO and D2CO have been measured under collisionless conditions. The H2CO 41 lifetimes vary at least a factor of 150, from 20 nsec to 3.10 μsec. The observed D2CO 41 lifetimes fluctuate about ±20% around a mean value of 6.2 μsec, which is probably close to the pure radiative lifetime. In contrast, the observed D2CO 43 lifetimes vary from 1.09 to 2.46 μsec and the 2143 lifetimes vary from 212 nsec to 1.61 μsec. The onset of rotational state lifetime fluctuations in D2CO thus coincides with the high pressure D2+CO photochemical threshold. All of these results are explained in terms of a collisionless sequential decay mechanism, S1→S0→H2(D2)+CO. The last step probably involves tunneling through a barrier for the lower energies studied. For several H2CO 41 rotational levels application of a uniform external electric field of 0–4.6 kV/cm can change the fluorescence lifetime by at least a factor of 4. This result is understood in terms of small (≲0.05 cm−1) shifts in S1−S0 energy spacings. Quantitative estimates of S1−S0 intramolecular couplings, S0 widths due to dissociation, and S0 level spacings are derived in favorable cases.

Electric field dependence of collisionless, single rotational level lifetimes of S1 H2CO

A glass fluorescence cell with two stainless steel stark electrode disks was used to measure the time decay of the fluorescence intensity of formaldehyde. (AIP)

Selected rotational level lifetimes and singlet-triplet coupling in the S 1 state of glyoxal

The fluorescence collision-free lifetimes were measured for a few rotational levels of the O° S 1 state of glyoxal using a single-mode Ar + laser. Decays are exponential over 5–6 lifetimes and variation of τ 1.k o does not exceed 5%. The higher limit of singlet-triplet mixing coefficient β 2 ⩽ 3 × 10 −2 is deduced from the lifetime measurements. The efficiency of collision induced intersystem crossing and its relation with <β 2 > value is discussed. ISC is absent in collision-free conditions for deuterated glyoxal as it is known to be for protonated glyoxal.

The feeding times and lifetimes of high-spin levels in ytterbium doubly even isotopes

The intensities, lifetimes and feeding times of rotational bands with spins up to 10–20ħ have been measured for four doubly even isotopes, 160–166Yb, formed in the reactions 124–130 52Te ( 40 18Ar, 4n), using the recoil-distance Doppler-shift method. The obtained values of rotational level lifetimes, τ I , are compared with the predictions of the rigid-rotor model. For the isotopes 164, 166Yb a small retardation (by a factor of 1.2–1.4) of transitions in the backbending region is found. Intrinsic quadrupole moments and deformation parameters are deduced as a function of spin for all the four isotopes. The results are discussed in terms of different backbending concepts. The meansquare angular momenta of the levels populated are obtained. Some conclusions on the nature of the γ-ray cascade leading to the feeding of rotational bands are drawn.

Lifetime of the a 3II Metastable State of Carbon Monoxide

The rotational dependence of the lifetime of the a 3II metastable state of CO has been investigated using a time-of-flight technique. The velocity distribution of metastable molecules is sampled and detected at two positions, 1.9 and 6.7 m from the pulsed electron gun used to excite the ground state molecules effusing from a cooled source slit. The initial population distribution among rotational levels is changed by varying the temperature of the source. A comparison of the number of metastables within given velocity intervals at the two detectors determines the number which decay in flight and yields an experimental plot of the number which decay versus time of flight. A theoretical decay plot is also obtained using the a 3II metastable state lifetimes calculated by James, who predicts rotational level lifetimes ranging from 3 msec to several hundred msec. For two different source temperatures, the experimental and theoretical decay plots are in good agreement.

Measured Lifetimes of Rotational and Vibrational Levels of Electronic States of N2

The lifetimes of vibrational levels of the B 3πg and C 3πu electronic states of molecular nitrogen and of the B 2Σu+ electronic states of the positive molecular nitrogen ion were measured by photometrically monitoring the excited level number densities in a pulsed invertron. Heavy-particle pressure damping cross sections were obtained from experimental studies of the pressure dependence of the reciprocal lifetimes. Lifetimes of individual rotational levels from K = 14 to K = 35 of the B 2Σu+(υ = 0) levels were measured. The lifetimes of all rotational levels were identical. However, our results suggest a dependence of the line strength on the rotational level different from that predicted by the Born–Oppenheimer approximation with zero rotational–vibrational interaction and zero electron spin–rotational interactions.