High Frequency Deflection Technique Research Articles

Lifetimes of Excited Levels in Some Important Ion-Molecules, Part III: CS+, COS+

Lifetimes of the recently discovered B-A system in CS+ and of the à - X̃ system in COS+ have been studied using the High Frequency Deflection Technique. The measured CS+ lifetime (425 ns) supports the identification of the B-A system by comparisons with CO+. Different lifetimes are found for the (0, 0, 0) à 2Π3/2 and à 2ΠA1/2 levels in COS+ (105 ± 3 ns and 77 ± 3 ns respectively), which shows that the earlier discovered predissociation is different for the two levels.

Experimental and Theoretical Studies of OD A2Σ+ State Lifetimes and Predissociations

Lifetimes of 160 different spin-splitted rotational levels of the OD A2Σ+ state (ν = 0-3) have been measured at high spectral resolution using the High Frequency Deflection technique. From these data the variation of the electronic transition moment is deduced as well as the predissociation rates for levels above the dissociation limit. These rates are compared to calculated ones based upon spin-orbit coupling between the crossing 2Σ+ and 4Σ- states. From a least square fit to the predissociation rates a potential crossing point slightly above ν = 5 of the A state at r = 1.50 ± 0.02 Å, and a spin-orbit coupling element Hso = 36 ± 18 cm-1 are found.

Radiative properties of the B 2Σ + and C 2Σ + states in OH and OD

Radiative lifetimes and relative intensities have been measured for the B—A and C—A systems in OH and OD using the high frequency deflection technique. The measured B state lifetimes, 2–3 μs, are affected by dissociative collisional transfer in similar ways as the A state, while the C state lifetimes (around 4 ns) are consistent with the description of the C state as an ionic state. The Boltzmann distribution on the B—A emission shows two components with T = 120 and 390 K. Revised calculations of Franck—Condon factors are included.

The Influence of Collisional Transfer Effects on Measured C2 Swan Band Transition Probabilities

Lifetimes and relative intensities of the C2 (d-a) Swan bands have been remeasured using the High Frequency Deflection technique, yielding τ(d, ν = 0-6) = 120 ± 4 ns. With increasing pressure of the C2H2 target gas strong second lifetime components occur revealing collisional transfers from other C2 levels with rate coefficients around 6 × 10-11 cm3 s-1 mol-1. These transfers are also observed with a number of other catalyser gases such as He, Ne, Ar, N2, and CO2. The transfer processes explain the considerably longer lifetimes reported in several earlier life-time investigations and could be a clue to the formation mechanism of the carbon high pressure bands.

Time Resolved Studies of the Interactions Between the A and B States in N2+

Spectra and lifetime of bands of the B-X emission system in N2+ (υ' = 0-3) have been studied at high spectral resolution using the High Frequency Deflection technique. From the results for higher υ' an accurate estimate of the variation of transition moment is established which is contradictory to most earlier results. The influence of the interactions with the A state is observed both as mixings in the B state lifetime at the spectroscopically known perturbations and collisional transfers which yield a continuously increasing lifetime for higher rotational levels of υ' = 0. An earlier observed anomaly in the lifetimes of υ' = 0, N' = 31 and 32 is shown to be caused by blending and the existence of a 4Σu+-X2 Σg+ system is discussed in view of time resolved studies of the isotopic 14N15N+B-X (0, 0) band.

Time resolved studies of collisional transfer and radiative decay of the CS A 1Π state

The lifetimes of the ν′ = 0–5 levels originating from the CS A 1Π state have been studied at high spectral resolution using the high frequency deflection technique. In addition to the well-known effects of triplet—singlet perturbations on the lifetimes, a strong sensitivity to large collisional transfers from more distant triplet levels have been revealed. The latter causes long-lived components in the decay curves and large increases of the AX band intensities when foreign catalyser gases are added.

Collisional Transfer to the B State in N2

Time-resolved spectra and intensities of the different vibrational bands from the B3Πg-A3Σ+u of N2 have been measured as a function of pressure using the High Frequency Deflection technique. Both the pressure of nitrogen and added catalyst gases (He, Ne and Ar) were varied from 0.6 to 20 m torr. In the case of v' = 6, 7, 11 and 12 strong pressure effects were noted both for the apparent lengthening of lifetimes and increase in intensities. Little or no pressure effects were seen for v' = 2, 3, 4, 5, 8, 9 and 10. These results have been explained in terms of resonance collisional transfer in which a metastable state is transferred through collison to the B state. The total collisional transfer rate coefficient to the B state was determined to be approximately 10-10 cm3 s-1, molecule. Data on the lifetimes extrapolated to zero pressure were used to derive the oscillator strength: f00abs = 1.69 ± 0.15 × 10-3.

New predissociations of the A state in SiH and their use in deriving an improved value of the dissociation energy

An exhaustive high-resolution study of the lifetimes of the A 2 Delta state of SiH has been made for a number of rotational levels of the v'=0, 1 and 2 progressions using the high-frequency deflection technique. From these results, together with a close comparison of similar results on the analogous A 2 Delta state in CH, evidence is given for predissociation following direct vibrational coupling with the X 2 Pi ground state, and the dissociation energy for SiH is determined as D0o=26950+or-200 cm-1. In addition, the lifetime values have been used, together with Franck-Condon factors to establish a small variation of the transition moment, and the absorption oscillator strength for the A-X (0,0) band is determined as f(0,0)=(4.98+or-0.15)*10-3.

The Influence of Collisional Transfers and Perturbations on Measured A and B State Lifetimes in CN

Lifetimes of a number of the red and violet CN bands have been studied at high spectral resolution using the High Frequency Deflection technique. While the result for the violet bands essentially supports earlier results, it is found that the lifetimes as well as the intensities of the red bands are strongly perturbed by processes which are suggested to be collisional transfers from X levels to near-lying A levels. These effects remain if additional catalyser gases are added to the ordinary C2N2 gas target and the increase of the A-X lifetimes and band-intensities depends on the polarizibility of the added gases. Simple models are presented for the time-resolved case as well as the steady state case from which the coefficient for the transfer rate is found to be of the order 10-10-10-11 cm3/s, mol. The new oscillator strengths for the red system corrected for the transfer effects are notably higher than earlier estimates and the astrophysical consequences of this are briefly discussed.

Correlation between perturbation and collisional transfers in theA, B, C andb states of CO as revealed by high resolution lifetime measurements

Lifetimes and intensities of theA-X, B-A, C-A andb-a systems in CO have been measured at high spectral resolution using the High Frequency Deflection technique. Of special interest are the pressure effects observed in theA-X andb-a transitions, both as a function of the partial pressure of CO and as a function of added catalyst gas such as argon, helium and CO2. The nature of these pressure effects are examined with the conclusion that resonance induced collision exchange takes place between theA orb states and other states that strongly perturb them. In particular, the collision exchange cross section estimated for theA state is unusually large, being the order of 10−7 to 10−8 cm3/s, mol. In contrast, theB andC (Rydberg) states, which are not known to be highly perturbed, showed no evidence of collision induced exchange. In addition, calculations on Franck-Condon factors and ¯r centroids have been carried out for each of the bands studied. Transition moments and oscillator strengths are also extracted from these calculations and from the new data presented in this paper, and considerable discrepancies to earlier values in the literature are found in some cases.

Precision Estimates of the Predissociation Rates of the OH A2Σ State (v ⩽ 2)

The lifetimes of 108 different rotational levels of the OH A state (υ = 0-2) have been measured at high spectral resolution using the High Frequency Deflection technique. From these lifetimes the variation of the electronic transition moment is deduced as well as the predissociation rates for levels above the dissociation limit and the formation rate of OH through inverse predissociation.

Trapping of Non-Resonance Radiation in Atoms and its Influence on Measured Lifetimes of the 4p and 5p Levels in Ar I

Lifetimes of 17 levels of the 3p5 4p and 3p5 5p configurations in Ar I have been measured using the High Frequency Deflection technique at target pressures in the range 0.04-10 mtorr. An anomalous pressure dependence is found which indicates that the studied 4p, 5p → 4s (non-resonance) transitions are subjected to trapping effects which occur because of exceptionally long lifetimes of the 4s levels due to either 4s → 3p resonance trapping (4s, J = 1) or metastability (4s, J = 0, 2). A theoretical fit to the observed pressure dependence based upon this process is given as well as corrected zero pressure lifetimes which in several cases are considerably shorter than earlier published values.

Lifetimes of Some Levels in Neutral Carbon, Nitrogen and Oxygen

Radiative lifetimes of a number of transitions to excited levels in neutral C, N and O have been directly measured using the High Frequency Deflection technique. With one exception, these lifetimes have not been experimentally studied earlier. The results are compared to Coulomb approximation calculations and to semi-empirical estimates as well as to very recent calculations including configuration interactions. A number of these visible and near infrared transitions have been utilized for estimating the solar C, N, and O abundances, and slight modifications are now suggested in some cases in view of the new f-values.

DBLCON: A version of positronfit with non-Gaussian prompt for analysing position lifetime spectra

Lifetime of eight levels belonging to the 4p45d configuration of singly ionized krypton have been measured by high-frequency deflection technique with a delayed coincidence single photon counting arrangement. The results have been compared with other experimental and theoretical values. The lifetimes of the 5d4P1/2, 5d′2D3/2, 5d′2F5/2, 5d2P3/2 and 5d2P1/2 levels have been measured for the first time.

Recent Advances in Studies of Molecular Transition Probabilities

The development of high power electron excitation applied in the High Frequency Deflection technique has enabled time resolved precision spectroscopy to be performed with a resolving power as high as 1:105. This is typically a two orders of magnitude higher resolution than what is commonly achieved using other approaches and this has created new possibilities of studying hitherto unknown properties of fundamental molecules. Thus a great number of time resolved studies of individual rotational levels including resolved spin-orbit and Λ components show that radiationless destructions of molecules are much more common in nature than earlier believed implying a violation of the Born Oppenheimer approximation which demands new theoretical treatments of molecular structure. Among important applications of the radiationless processes should be mentioned determinations of dissociation energies with superior accuracy and molecular formation rates. An extensive programme for theoretical studies of the obtained results is in progress in collaboration with the quantum chemistry groups in Århus and Uppsala. This programme also includes precision estimates of oscillator strengths with applications to molecular abundance estimates and to laser physics.

Lifetimes of Excited Levels in Some Important Ion-molecules. Part II: O2+

The spectra and lifetimes of the b 4Σg--a 4Πu and A 2Πu-X 2Πg systems in the O2+ molecule have been studied at high resolution using the High Frequency Deflection technique. The measured lifetimes are found to be 30-50% longer than earlier results which are shown to be distorted by Coulomb repulsion effects. The variations of the transition moments are established for both the systems using recently calculated q and r̄ values and an upper limit of 105 s-1 is found for predissociations of the b state.

Predissociation Rates and Perturbations of the A, B, B', C, D and F States in NO Studied Using Time Resolved Spectroscopy

Radiative lifetimes of the A2Σ+, B2Π, B'2Δ, C2Π, D2Σ+ and F2Δ electronic states in NO have been measured at high spectral resolution using the High Frequency Deflection technique. Particular attention has been paid to levels in the vicinity of or above the first dissociation limit in order to search for predissociation effects. The well-known effect in the C state is confirmed, while new predissociations of the A and D states and their rates are established. An anomaly in the lifetime series (B', v = 0-5) at v = 4 is explained in terms of the B'(v = 4) ∼ F(v = 1) configuration interaction. The variation in the A-X transition moment has been measured and found to be substantially different from earlier estimates.

The D state lifetime and the UV laser action of molecular iodine

Abstract The lifetime of the D 1 Σ + u state of I 2 has been measured using the high frequency deflection technique; from the result (15.5 ± 0.5 ns), absolute rates are determined for the transfer of this state to the lasing 3 H 2g state by collisions with Ne, Ar and CF 4 .

Radiative Lifetimes of Resonance Levels in Fel I and Fe II

Lifetimes of various J-levels of low lying resonance levels in Fe I and Fe II have been measured at high spectral resolution using the High Frequency Deflection technique. The results are compared with earlier results and recommended multiplet f-values are given for astrophysical abundance determinations.

Direct Measurement of the N2+ C State Predissociation Probability

The lifetimes of the vibrational ν = 1-5 levels of the N2+ C state have been directly measured at high resolution using the High Frequency Deflection technique. For the ν = 2 level, a radiative lifetime τ = 78.9 ± 3.0 ns is obtained, while the lifetimes drop sharply to a constant value of 4-5 ns for the ν ⩾ 3 levels. Since the ν ⩾ 3 levels are all above the lowest dissociation limit, the measurements confirm that these levels are predissociated and at a rate of about 2 × 108 s-1. The lifetime variation suggests that the predissociation mainly takes place through vibrational coupling with the B state.