Chlorine Atom Formation Dynamics of NOCl and $PCl_3$ at 222 nm: The dissociation dynamics of NOCl and ${ PCl}_3$ after UV photoexcitation at 222 nm have been investigated. Total and relative quantum yields of Cl($^{2}P_{3/2}$) and $Cl*(^{2}P_{1/2}$) atoms were determined using the laser photolysis/vacuum-UV laser-induced fluorescence technique. The total quantum yield for chlorine atom formation of $PCl_3$ was determined to be 0.76±0.13. The relative Cl* quantum yields were found to be 0.36 (NOCl) and 0.53 ($PCl_3$), respectively. The nearby triplet state, as well as the singlet state $S_5 (4^1A`)$, seems to contribute to the A band absorption of NOCl. It is concluded that the dissociation process of PCl3 yielding ground state $PCl_2$(${\tilde X}^{2}B_1$) and Cl/Cl* is dominant at 222 nm photolysis.
Dynamics of the H+HCl reaction at 1.4 eV: The dynamics of the gas-phase H+HCl reaction has been investigated at an average center-of-mass collision energy of 1.4 eV. The laser photolysis/vacuum-UV laser-induced fluorescence technique coupled with a sum-difference frequency conversion scheme was employed to determine the absolute reaction cross-section for spin-orbit ground state Cl atom formation and the spin-orbit branching ratio between Cl and Cl*. A photolytic calibration method was used as a source for well-defined concentrations of Cl and Cl*. The absolute reaction cross-section has been found to be $σ_R^{Cl} (1.4eV) = 0.24±0.03 Å^2$. This coincides well with the theoretical predictions and other experimental observations. Small but apparent signal of Cl* from the reaction was observed, leading to the branching ratio of $β _{Cl*} = 0.07±0.01$. This implies that the nonadiabatic transition leading to Cl* formation in the exit channels of the exchange reaction is not negligible at high collision energies.
Detection of OH Radicals in a Butane/Air Flame: DFWM has been employed to detect OH radicals in a butane/air flame. The fully resonant wave-coupling process generates the signal that is bright enough to be isolated from the background noises of the highly irradiant source. The collimated nature of the resultant signal facilitates the remote sensing of the high temperature flame. The temperature of the butane/air flame has been determined by extracting OH internal state distribution from the spectrum and by fitting the nascent rotational distribution with a Boltzmann function. The saturation behavior of the signal has also been investigated for the $Q_1$(6) line.
Photodissociation Dynamics of Formic Acid at 212.8 nm: Degenerate four-wave mixing spectroscopy has been utilized to investigate the photodissociation dynamics of formic acid. Room temperature formic acid was excited at 212.8 nm, near the absorption maximum of the $^1(n,π*)_{C = O}}$. The background-free rotational spectrum of the nascent OH radicals was obtained. The OH radicals were found to be populated exclusively in the electronic and vibrational ground state. A cold rotational energy distribution of OH peaking at N"=3 was extracted from the DFWM spectrum. The distribution was approximated well by a Boltzmann distribution with a rotational temperature of $T_{rot} ~ 716 K$, which corresponds to the average rotational energy of ca. $498±1 cm^{-1}$. Vector correlations were also inspected, and no significant rotational alignment and recoil anisotropy were verified. The non-statistical spin-orbit state distribution with a preference of the low-energy $F_1$ manifold implies absence of any interactions with nearby triplet state(s) during dissociation. The preferential population of ∏(A`) $\Lambda$-doublet was observed, which suggests that the $ν_7$ H-O-C bending vibration in HCOOH($\tilde A$) and recoil impulse are a main source for the rotational energy of OH.
Photodissociation Dynamics of Alkyl and Perfluoroalkyl Iodides at 266 nm: Two-photon resonant four-wave mixing spectroscopy has been utilized successfully for probing I and I* nascent from the 266-nm photodissociations of various alkyl and perfluoroalkyl iodides. The relative quantum yields for I*, as well as the recoil anisotropy parameters, were extracted. Recoil anisotropy parameters close to the limit value for parallel transition indicates that the ground-state I($^2P_{3/2}$) originates from the curve crossing from the initially prepared $^{3}Q_{0}$ to $^{1}Q_{1}$ state. The curve-crossing probabilities for alkyl and perfluoroalkyl iodides were obtained. It has been revealed that the electronic effect due to fluorine atom substitution is dominant, leading to decrease in the curve crossing probability. TP-RFWM has proved to be a very useful tool for diagnosis of atomic species in low concentration sample. This scheme can be used for the remote detection of a variety of atomic species in hostile environments such as plasma and flames.
Photodissociation Dynamics of Acetyl Bromide at 234 nm: The photodissociation dynamics of acetyl bromide was investigated at 234 nm. A 2-dimensional photofragment ion-imaging technique coupled with a [2+1] resonance-enhanced multiphoton ionization scheme was utilized to obtain speed and angular distributions of the nascent Br($^{2}$P$_{3/2}$) and Br*($^{2}$P$_{1/2}$) atoms. The recoil anisotropies for the Br and Br* channels were measured to be $β = 1.47±0.05$ for Br and 1.44±0.05 for Br*. The relative quantum yield for Br* was found to be $Φ_{Br*} = 0.37±0.05$. The probability of nonadiabatic transition between two A` states was determined to be 0.36. Broad Gaussian distributions were observed for the total translational energy distributions corresponding to the Br and Br* channels. The soft radical limit of the impulsive model adequately modeled the related energy partitioning. It is proposed that the σ* ← n transition localized on the C-Br chromophore mainly contributes to the initial transition of acetyl bromide at 234 nm.
다양한 대기 중의 광화학 반응과 분자 구조를 규명하는 데 있어 광분해 동력학의 연구는 필수적이다. 본 연구에서는 레이저를 응용한 비선형 분광학 기법을 바탕으로 광분해 반응에 의해 생성된 광분해체를 관측하고 그들의 양자 상태 분포 및 벡터량을 측정하였다.
합-차 파장 변환을 응용하여 진공 자외선 영역의 탐사광을 생성시켜 NOCl 및 $PCl_3$ 분자들의 222 nm에서의 광분해 결과 생성된 염소 원자의 양자 상태 분포를 측정하였다. 또한, 대기 중의 화학 반응 및 내연 기관 내부에서의 산화 반응에 기초가 되는 H+HCl 반응을 통해 생성된 염소 원자의 상대적 양자 수율을 측정하였다.
축퇴 사광파 혼합 분광학을 이용하여 부탄과 공기의 혼합물로 이루어진 화염계에 존재하는 하이드록실 라디칼의 회전 양자 상태 분포를 측정하고, 이로부터 열적 평형 상태의 화염의 온도를 측정하였다. 또한, 포름산 단일체의 212.8 nm에서의 광분해 결과 생성된 하이드록실 라디칼의 스칼라 및 벡터량을 측정하였다. 포름산 단일체의 광분해 동력학은 카르복실기를 포함한 모든 유기물질의 광분해 현상에 대한 기초적 모델을 제공한다. 이광자 공명 사광파 혼합 분광학을 응용하여 요오드화 알칸의 266 nm에서의 광분해 반응에 의해 생성된 요오드 원자를 상태 선택적으로 관찰하였다. 또한, 요오드 원자의 공간적 분포로부터 벡터 상관관계에 대한 정보를 추출함으로써, 요오드화 알칸의 광분해 과정을 포텐셜 에너지 표면 교차 현상으로써 설명하였다.
공명-강화 다광자 이온화 분광학을 응용하여 아세틸 브로마이드의 234 nm에서의 광분해 결과 생성된 브롬 원자를 관측했다. 브롬 원자의 공간적 분포와 각 스핀-궤도 상태의 상대적인 양자 수율로부터 자외선 영역에서의 아세틸 브로마이드의 동력학적 거동이 규명되었다. 본 연구 결과를 바탕으로 $C_s$ 대칭구조를 지닌 분자의 비단열적 동력학 현상에 대한 모델이 제시되었다.
