TY - JOUR
T1 - The νCC+3νCH rovibrational manifold of acetylene. I. Collision-induced state-to-state transfer kinetics
AU - Milce, Angela P.
AU - Orr, Brian J.
PY - 1997/3/1
Y1 - 1997/3/1
N2 - Infrared-ultraviolet double resonance (IR-UV DR) spectroscopy is used to measure collision-induced, rotationally resolved state-to-state energy transfer in the νCC+3νCH vibrational manifold of gas-phase acetylene, C2H2. Attention focuses on three sets of vibrational eigenstates spectroscopically labeled (0 1 3 0 0)0
I, (0 1 3 0 0)0
II, and (0 4 0 3 3)0
+, with vibrational term energies in the region 11 585-11 600 cm-1. IR-UV DR spectroscopy identifies the channels of J-changing rotational energy transfer (RET) and inter-mode vibrational (V-V) transfer. The second-order state-to-state kinetics of these channels is measured by scanning the IR-UV pulse delay with the IR PUMP and UV PROBE lasers tuned to particular spectroscopic features. There is a clear propensity for even-numbered changes ΔJ of rotational quantum number in the observed RET and V-V transfer, consistent with conservation of ortho or para nuclear-spin symmetry in the state-selected C2H2 molecule, but there are some notable exceptions as unusual symmetry-breaking processes result in odd-ΔJ V-V transfer. Anomalies of this type have been investigated in a preceding paper [A. P. Milce and B. J. Orr, J. Chem. Phys. 104, 6423 (1996)]. A detailed IR-UV DR study is made with the UV PROBE laser monitoring the (0 4 0 3 3)0
+, J=12 rovibrational level; RET is measured when the IR PUMP laser prepares molecules in various J-states of (0 4 0 3 3)0
+, while V-V transfer is monitored when initial J-states of (0 1 3 0 0)0
I or (0 1 3 0 0)0
II are prepared by the IR PUMP. The corresponding IR-UV DR kinetic curves are fit to a detailed rate-equation model in which empirical exponential-gap fitting laws are used to describe even-ΔJ channels of RET and V-V transfer. It is remarkable that the kinetics of symmetry-breaking odd-ΔJ V-V transfer between the (0 1 3 0 0)0
I, J=5 and (0 4 0 3 3)0
+, J=12 rovibrational levels is well fit by the same model. The dynamical implications of these results are discussed.
AB - Infrared-ultraviolet double resonance (IR-UV DR) spectroscopy is used to measure collision-induced, rotationally resolved state-to-state energy transfer in the νCC+3νCH vibrational manifold of gas-phase acetylene, C2H2. Attention focuses on three sets of vibrational eigenstates spectroscopically labeled (0 1 3 0 0)0
I, (0 1 3 0 0)0
II, and (0 4 0 3 3)0
+, with vibrational term energies in the region 11 585-11 600 cm-1. IR-UV DR spectroscopy identifies the channels of J-changing rotational energy transfer (RET) and inter-mode vibrational (V-V) transfer. The second-order state-to-state kinetics of these channels is measured by scanning the IR-UV pulse delay with the IR PUMP and UV PROBE lasers tuned to particular spectroscopic features. There is a clear propensity for even-numbered changes ΔJ of rotational quantum number in the observed RET and V-V transfer, consistent with conservation of ortho or para nuclear-spin symmetry in the state-selected C2H2 molecule, but there are some notable exceptions as unusual symmetry-breaking processes result in odd-ΔJ V-V transfer. Anomalies of this type have been investigated in a preceding paper [A. P. Milce and B. J. Orr, J. Chem. Phys. 104, 6423 (1996)]. A detailed IR-UV DR study is made with the UV PROBE laser monitoring the (0 4 0 3 3)0
+, J=12 rovibrational level; RET is measured when the IR PUMP laser prepares molecules in various J-states of (0 4 0 3 3)0
+, while V-V transfer is monitored when initial J-states of (0 1 3 0 0)0
I or (0 1 3 0 0)0
II are prepared by the IR PUMP. The corresponding IR-UV DR kinetic curves are fit to a detailed rate-equation model in which empirical exponential-gap fitting laws are used to describe even-ΔJ channels of RET and V-V transfer. It is remarkable that the kinetics of symmetry-breaking odd-ΔJ V-V transfer between the (0 1 3 0 0)0
I, J=5 and (0 4 0 3 3)0
+, J=12 rovibrational levels is well fit by the same model. The dynamical implications of these results are discussed.
UR - http://www.scopus.com/inward/record.url?scp=0345845098&partnerID=8YFLogxK
U2 - 10.1063/1.473466
DO - 10.1063/1.473466
M3 - Article
AN - SCOPUS:0345845098
SN - 0021-9606
VL - 106
SP - 3592
EP - 3606
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
IS - 9
ER -