Anomalous light-induced drift of linear molecules |
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Authors: | A I Parkhomenko |
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Institution: | (1) Institute of Automation and Electrometry, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia |
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Abstract: | The sudden approximation in energy is used to derive analytic formulas that describe the anomalous light-induced drift (LID)
of linear molecules absorbing radiation in the rovibrational transition nJ
i
−mJ
f
(n and m are the ground and excited vibrational states, and J
α
is the rotational quantum number in the vibrational state α=m, n). It is shown that for all linear molecules with moderate values B≲1 cm−1 of the rotational constant, anomalous LID can always by observed under the proper experimental conditions; temperature T, rotational quantum number J
i
, and type of transition (P or R). The parameter γ=BJ
i
(J
i
+1)−J
f
(J
f
+1)] ν
n
/2k
BT
(ν
m
−ν
n
) is used to derive a condition for observing anomalous LID: γ∼1 (k
B
is the Boltzmann constant and ν
α
is the transport rate of collisions of molecules in the vibrational state α and buffer particles at moderate molecular velocities
, where
is the most probable velocity of the buffer particles). For ν
m
>ν
n
anomalous LID can be observed only in P-transitions, while for ν
m
<ν
n
it can be observed only in R-transitions. It is shown that anomalous LID is possible for all ratios β=M
b
/M of the masses of the buffer particles (M
b
) and of the resonant particles (M) and any absorption-line broadening (Doppler or homogeneous). The optimum conditions for observing anomalous LID are realized
when the absorption line is Doppler-broadened in an atmosphere of medium-weight (β∼1) and heavy (β≫1) buffer particles. In this case, anomalous LID can be observed in the same transition within a broad temperature interval
ΔT∼T. If the buffer particles are light (β≪1) or if the broadening of the absorption line is homogeneous, anomalous LID in the same transition can be observed only
within a narrow temperature range ΔT≪T.
Zh. éksp. Teor. Fiz. 115, 1664–1679 (May 1999) |
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Keywords: | |
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